Connect a Dehumidifier to a Sump Pump: 3 Safe Methods

Emptying a heavy dehumidifier bucket every day quickly becomes a chore in a damp basement or crawl space. When you connect a dehumidifier to a sump pump system, you route the continuous-drain hose directly into the sump basin—never into the pump motor itself—so your existing float-activated sump pump automatically expels the collected moisture outdoors.

Quick Answer

To connect a dehumidifier to a sump pump, run a drain hose into the sump basin using one of three methods: slope a 3/4-inch garden hose continuously downhill for gravity drainage, use the dehumidifier’s built-in pump tubing for vertical rises up to 16 feet, or install an external condensate pump. Secure the hose end above standing water and clear of the sump float switch.

At a Glance

Time Required	15 to 30 minutes for gravity or built-in pump drainage; 45 to 60 minutes when adding an external condensate pump or sealed lid port
Difficulty	Easy for direct gravity or built-in pump routing; moderate when installing a condensate pump or sealing a radon sump cover
Tools Needed	1/2-inch or larger garden hose (or manufacturer pump tubing), rubber hose washer, hose clip or strap, utility knife, screwdriver, and airtight grommet for sealed lids

Why Use a Sump Pump With a Dehumidifier

Dehumidifier drain hose routed across a basement floor to connect a dehumidifier to a sump pump basin

Routing dehumidifier condensate into a sump basin lets the unit run continuously without shutting off for manual bucket emptying. Water trickles or pumps into the pit, and your existing submersible or pedestal sump pump discharges it outside whenever the rising water level lifts the float switch.

This setup works well in damp basements, laundry rooms, and crawl spaces that lack a nearby floor drain. According to ENERGY STAR, dehumidifiers can drain continuously through a hose directed to a floor drain or sump pit, removing the need to empty the collection bucket by hand. Even a high-capacity 50-pint dehumidifier adds only about 6 gallons of water per day at peak extraction, which triggers just one or two brief sump cycles.

Continuous drainage only removes moisture already in the air; it will not fix a foundation crack, failed vapor barrier, clogged gutter, or plumbing leak. The U.S. Environmental Protection Agency recommends maintaining indoor relative humidity below 60%—and ideally between 30% and 50%—while repairing the underlying source of water intrusion. If your sump pit has no cover at all, adding a fitted lid around the pipes also prevents standing pit water from evaporating right back into the basement air.

A sump pump removes water from the sump basin. It does not provide an intake fitting for attaching a dehumidifier hose directly to the pump body.

Choose Gravity Drainage, a Built-In Pump, or a Condensate Pump

Your drainage method depends on two factors: whether the sump opening sits lower than the dehumidifier’s drain port, and whether your dehumidifier includes a built-in pump. Compare the elevation of the drain port against the path to the sump basin before buying extra parts.

Drainage Method	When to Use It	Typical Hose or Tubing	Vertical Lift Limit
Option 1: Direct Gravity	Sump rim is lower than the drain port and the entire hose route slopes downhill	Standard 3/4-inch female GHT garden hose (at least 1/2-inch inner diameter)	0 ft (must slope downhill continuously)
Option 2: Built-In Pump	Hose must rise over an obstacle or travel across the room on a pump-equipped unit	Manufacturer-supplied 1/4-inch or 3/8-inch plastic pump tubing	Up to 14–16 ft (typically 16 ft max tube length)
Option 3: Condensate Pump	Route must rise or cross obstructions and the dehumidifier lacks an internal pump	Short gravity hose to reservoir + 3/8-inch ID clear vinyl discharge tubing	10–15 ft working lift (17–20 ft shutoff head)

Option 1: Direct Gravity Drainage

Use direct gravity drainage whenever the sump basin opening sits lower than the dehumidifier’s drain port and the hose can slope downward along its entire path. Gravity drainage is the simplest, most reliable method because it uses no extra motor or float switch. For fitting visuals, see our guide to connecting a dehumidifier drain hose step by step, read can you drain a dehumidifier into a sump pump for system compatibility, and check draining a dehumidifier using a hose or gravity for elevation tips.

To drain reliably by gravity, the hose must:

Thread onto the dehumidifier’s continuous-drain outlet (typically a 3/4-inch male garden-hose thread) with a rubber sealing washer.
Remain below the drain outlet from start to finish without upward loops, humps, or crushed sections.
Terminate securely inside the sump basin well away from the sump-pump float switch.
Stay above the normal standing-water line in the pit so air can escape and water does not back up.

Frigidaire’s drainage guidance recommends using a garden hose at least 1/2 inch in diameter—keeping it below the connection port, flat, and free of kinks—because narrow hoses clog easily with dust and algae sludge.

Option 2: Use the Dehumidifier’s Built-In Pump

If the hose must rise over a doorway, pipe, or raised sump rim, check whether your dehumidifier already includes an internal condensate pump. A pump-equipped model pushes water uphill through narrow pressurized tubing, eliminating the need to buy a separate external pump.

Follow your model’s specific pump rules. According to GE Appliances’ dehumidifier drainage guidance, built-in drain pumps can lift water up to 16 vertical feet into a sump basin through the supplied 16-foot hose, provided the internal bucket stays seated in place and pump mode is activated (often by holding the Pump button for 3 seconds). Never extend the factory pump tubing beyond its rated 16-foot length, or backpressure may cause the pump to fail.

Anchor the lightweight pump tubing at the sump rim so water pressure cannot whip the loose end out of the basin or tangle it in the sump float.

Option 3: Drain Through a Condensate Pump

Install a separate external condensate pump when gravity routing is impossible and your dehumidifier lacks a built-in pump. The external pump sits on the floor next to the dehumidifier, collects gravity-fed water in a small reservoir, and pumps it overhead or across the room to the sump basin.

In a standard condensate-pump setup:

The dehumidifier drains downward through a short hose into one of the condensate pump’s top inlet holes.
An internal float switch starts the condensate pump once the reservoir fills to its trigger depth.
The pump pushes water through 3/8-inch inner-diameter (ID) vinyl tubing and a one-way check valve into the sump basin.

Select a pump rated for HVAC or appliance condensate and verify its flow rate at your actual vertical lift, not just its shutoff rating. For example, the Little Giant VCMA-20 series uses a 1/2-gallon tank and a 3/8-inch barbed check-valve outlet. Its performance chart delivers 80 gallons per hour (GPH) at 1 foot of lift and 48 GPH at 10 feet, whereas its advertised 20-foot rating on the 115-volt model is the shutoff head where flow drops to zero.

Note: Never drill or tee small dehumidifier tubing directly into the sump pump’s rigid PVC discharge pipe. The 2024 International Plumbing Code (Section 314.2.1.1) prohibits connecting condensate drains directly into any plumbing drain, waste, or vent pipe, and pressurized sump discharge water can force its way backward into your dehumidifier. Also confirm that your sump pump’s outdoor discharge complies with local municipal rules, which commonly prohibit draining groundwater into sanitary sewers.

What You Need for the Drain Connection

Gather the correct hose, adapter, and securing hardware for your chosen drainage method before unplugging the appliance. Most portable dehumidifiers use a standard 3/4-inch male garden-hose thread for gravity drainage and a proprietary quick-connect or barbed port for internal pump tubing.

For Direct Gravity Drainage

A 1/2-inch or 5/8-inch ID garden hose (with a 3/4-inch female garden-hose thread) long enough to reach the sump pit without tension
A fresh rubber hose washer to seal the threaded connection
A thread adapter if your dehumidifier uses a non-standard drain nozzle
A hose clip, masonry clamp, or heavy-duty zip tie to anchor the hose at the sump basin
An airtight rubber grommet or bulkhead fitting if passing through a sealed sump lid

For Built-In Pump Drainage

The 1/4-inch or 3/8-inch pump tubing supplied with your dehumidifier (typically 16 feet long)
The factory push-to-connect or threaded pump adapter fitting
A mounting clip or strap to hold the tubing end inside the sump basin
A matching rubber grommet if routing through a sealed sump cover

For Condensate-Pump Drainage

An automatic condensate removal pump (115V, typically 1/30 HP with a 1/2-gallon reservoir)
A short gravity hose to connect the dehumidifier outlet to the pump reservoir inlet
20 feet of 3/8-inch ID clear vinyl discharge tubing
A 3/8-inch barbed check valve (usually pre-installed on the pump discharge port)
A stainless-steel worm-gear hose clamp or plastic snap clamp for the barbed fitting
Low-voltage wire if connecting the pump’s overflow safety switch to an alarm or shutoff circuit

Never force mismatched plastic threads together. Threaded garden-hose fittings seal against the flat rubber washer inside the female coupling—if a connection drips, replace the washer rather than overtightening with pliers and cracking the plastic drain spout.

Warning: Unplug the dehumidifier, condensate pump, and sump pump before routing hoses inside the sump basin. Plug all equipment directly into grounded, GFCI-protected wall receptacles kept off the floor and away from splash zones. Never use an extension cord or power strip with a dehumidifier or pump, as sustained current draw can overheat undersized cords.

Place the Dehumidifier and Drainage Equipment Correctly

Position the dehumidifier on a sturdy, level surface near the sump basin with at least 8 to 12 inches of airflow clearance around its air intake and exhaust grilles. If you need extra height for gravity drainage, elevate the unit on stable concrete blocks or a heavy-duty appliance stand.

Level Surface Placement

Both the dehumidifier and any external condensate pump must sit dead level so internal collection pans and float switches operate at their designed water depth. A tilted dehumidifier can spill condensate past its internal drain pan into the bottom bucket or onto the floor.

Check the top of the dehumidifier with a spirit level so it does not rock or lean away from the drain port.
Maintain full clearance around the washable air filter and exhaust vents.
Set an external condensate pump flat on the floor below the dehumidifier’s gravity spout.
Keep the sump lid, pump cords, and hose fittings accessible for routine cleaning.
Leave slight slack at each fitting so foot traffic or vibration cannot pull a hose loose.

Never set a dehumidifier directly on a low floor spot that floods if the sump pump loses power. Raising the appliance 6 to 12 inches on solid masonry blocks protects the electrical components and increases the downward slope for gravity drainage.

Downward Hose Path

Every gravity-fed hose—whether running straight to the sump pit or feeding a condensate pump—requires a continuous downward drop of at least 1/4 inch per foot. Even a 1-inch upward hump or coiled loop creates an airlock that traps water and forces condensate back into the dehumidifier bucket.

Route the hose along a wall base away from foot traffic, sharp metal edges, and hot water pipes. Clip long runs every 18 to 24 inches so flexible hose cannot sag and collect stagnant water.

Pro Tip: Before connecting the hose to the dehumidifier, hold the inlet end at the height of the drain port and pour two cups of clean water through it with a funnel. If water exits into the sump pit within a few seconds without pooling, your slope is ready.

Protect a Sealed or Radon-Mitigation Sump Lid

If your sump basin has a sealed cover connected to a PVC radon vent pipe, never prop the lid open or drill an unsealed hole for a drain hose. The EPA radon mitigation standards (Sections 14.5.1 and 14.7.4) require airtight sump covers, sealed caulking or grommets around all pipe and wire penetrations, and a trapped drain whenever surface or appliance water enters a radon-controlled sump pit.

An open gap or an untrapped dry hose allows the sub-slab radon fan to pull conditioned basement air into the pit—reducing negative pressure under the slab—or lets radon gas travel up the hose into your living space if the radon fan loses power. Pass the hose through a tight rubber grommet or bulkhead fitting sealed with 100% silicone caulk, and include a shallow water-retaining P-trap loop right at the lid entry (with the dehumidifier elevated above the top of the loop) or use a condensate pump equipped with a one-way check valve. Check your radon system’s U-tube manometer after sealing to verify sub-slab suction remains unchanged, or hire a certified radon mitigator to install the port.

How to Connect a Dehumidifier to a Sump Pump

Once your equipment is positioned and your hose path is clear, follow the steps below for your specific drainage setup. Always complete the mechanical routing and secure the sump basin end before plugging the unit back in.

Method 1: Connect Directly to the Sump Basin (Gravity)

Unplug the dehumidifier. Disconnect power before opening the drain port cover or handling the sump lid.
Uncover the continuous-drain port. Unscrew the plastic knockout or drain cap on the back or side of the unit, and install the manufacturer’s threaded drain adapter if required.
Seat the rubber washer. Press a clean rubber hose washer flat inside the female coupling of your garden hose.
Thread the hose onto the drain port. Turn the coupling clockwise by hand until snug; do not use wrenches that can strip plastic threads.
Route the hose continuously downhill. Lay the hose straight to the sump basin without loops, rises, or sharp bends.
Position the outlet inside the sump pit. Insert the hose end 2 to 3 inches inside the basin rim, keeping it above the standing water line and at least 4 inches away from the sump-pump float switch, tether arm, and intake screen.
Anchor the hose end. Fasten the hose to the basin lip or discharge pipe clamp with a heavy-duty zip tie or bracket so it cannot slip into the float path.
Plug in and test. Restore power, set your desired humidity level (40% to 50%), and inspect the threaded fitting for drips.

Method 2: Use the Dehumidifier’s Built-In Pump

Verify internal pump specifications. Confirm that your model has a dedicated pump port and check the manual for maximum lift and hose length (typically 16 feet).
Attach the factory pump tubing. Push the supplied 1/4-inch or 3/8-inch tubing firmly into the quick-connect pump outlet—or tighten the compression nut—until it locks in place.
Seat the collection bucket. Slide the internal water bucket fully into the cabinet, as most dehumidifiers draw pump water from the bucket or require its magnetic float switch to be engaged.
Route the tubing to the sump basin. Run the tubing without tight kinks, keeping the highest point within the unit’s vertical lift limit.
Secure the discharge end in the pit. Clip the tubing firmly inside the sump basin, clear of the sump-pump float and above standing water.
Activate pump mode. Plug in the dehumidifier and press the Pump button (hold for 3 seconds on many GE and Midea units) until the pump indicator light stays illuminated.
Run a full discharge test. Allow the unit to fill its reservoir (or pour clean water into the bucket) and verify the internal pump turns on, empties into the sump pit without spraying, and shuts off cleanly.

Method 3: Connect Through a Condensate Pump

Set the condensate pump in place. Position the pump reservoir flat on the floor below the dehumidifier’s gravity drain port.
Run the inlet hose. Remove one of the plastic knockouts on the top of the condensate pump and run a short, continuously downhill hose from the dehumidifier port about 1 inch into the reservoir hole.
Attach the 3/8-inch discharge tubing. Slide the clear 3/8-inch ID vinyl tubing over the pump’s barbed check-valve outlet and tighten a hose clamp over the barb.
Route the discharge line to the sump pit. Run the vinyl tubing up and over obstructions to the sump basin, staying well below the pump’s shutoff head limit.
Anchor the tubing inside the sump basin. Secure the discharge end inside the pit away from the sump float switch and above the water line so it cannot siphon backward.
Wire the safety switch (optional). If your condensate pump includes high-water overflow leads, connect them to a water alarm or your dehumidifier’s interlock circuit if supported.
Restore power to both units. Plug the condensate pump and dehumidifier into grounded GFCI receptacles.
Test automatic cycling. Pour clean water into the condensate pump’s open inlet hole until the float triggers the motor, confirming it pumps smoothly into the sump pit and stops without backflow.

Keep every gravity-fed hose continuously downhill. When using an internal or external pump, secure the lightweight discharge tubing at the sump rim so pump pressure cannot whip it into the float switch.

Test the Pump and Check for Leaks

Never leave a new dehumidifier drain setup unattended until you have tested the entire water path from the appliance to the outdoor sump discharge. Run a manual water test immediately after installation and recheck all fittings after 4 to 6 hours of operation.

Check	What to Confirm
Dehumidifier drain port	Water exits freely through the hose coupling without dripping from threads or overflowing into the bucket.
Gravity hose slope	Water flows steadily into the pit with no upward dips, kinks, or submerged hose end.
Built-in dehumidifier pump	Pump indicator light is active, the bucket is seated, and the pump cycles on and off without error codes.
External condensate pump	Adding water to the reservoir lifts the internal float, discharges water into the sump, and shuts off cleanly.
Sump-pump float clearance	The drain hose is tied back so it cannot touch or snag the sump float arm throughout its full travel.
Sump pump activation	Pouring a 5-gallon bucket of clean water into the pit raises the float, starts the sump pump, and empties the basin.
Radon lid seal	Any grommet penetration is airtight, the water trap holds prime, and the radon manometer reading is normal.

Never run a submersible sump pump dry to test its motor; always pour clean water into the sump basin until the float rises naturally. Check threaded couplings with a dry paper towel after several hours of dehumidification to catch slow seepage.

Troubleshoot a Dehumidifier That Will Not Drain

When water backs up into the dehumidifier bucket or leaks onto the floor, the cause is almost always an airlock from an uphill hose section, a missing rubber washer, or a clogged drain port. Use the table below to diagnose and fix the issue quickly.

Problem	Likely Cause	What to Do
Water still fills the bucket during gravity drainage	Hose has an uphill loop, outlet is submerged in pit water, unit tilts backward, or internal nozzle is clogged	Elevate the dehumidifier, remove hose dips, raise the hose end above pit water, and flush the drain port with warm water.
Drip at the threaded hose fitting	Missing or hardened rubber washer, cross-threaded coupling, or missing proprietary drain adapter	Unplug the unit, install a new rubber garden-hose washer, align the threads straight, and hand-tighten firmly.
Built-in pump does not discharge (or shows “PU” / “Eb” code)	Pump mode is off, bucket is not fully seated, tubing is kinked, or lift exceeds 16 feet	Enable Pump mode, reseat the bucket, clean the bucket pump pickup screen, and keep tubing under 16 feet.
Condensate pump runs continuously with weak flow	Pinched 3/8-inch vinyl tubing, algae blockage in check valve, or vertical lift near shutoff head	Unplug the pump, remove and rinse the barbed check valve, clear tubing kinks, and reduce vertical lift.
Condensate pump short-cycles every few minutes	Water in the vertical rise is flowing backward into the reservoir through a stuck check valve	Clean or replace the discharge check valve and ensure the arrow on the fitting points away from the pump.
Sump basin fills without sump pump starting	Tripped GFCI outlet, unplugged float piggyback plug, or dehumidifier hose pinning the float down	Reset the GFCI breaker, re-anchor the dehumidifier hose away from the float, and test the sump switch manually.
Slime buildup or musty odor in the drain line	Airborne dust and biofilm collecting in low-velocity condensate water	Flush the hose with warm water and a 1:1 white vinegar solution, and clean the dehumidifier air filter monthly.

If your sump basin connection is clear but water still bypasses the hose and fills the internal bucket, read why your dehumidifier is not draining through the hose for step-by-step internal port and float fixes.

Keep the Drain System Running Smoothly

Inspect your dehumidifier drain line and sump basin once a month during humid summer weather and immediately after any basement power outage or heavy storm. Airborne dust washed off the evaporator coils settles inside hoses and pump reservoirs, forming thick biofilm if left uncleaned.

Verify that the dehumidifier and external condensate pump remain level on their supports.
Inspect gravity hoses for sags, kinks, algae buildup, or items stacked on the line.
Check built-in pump tubing for brittle plastic, loose push-fittings, or sharp bends.
Flush the drain hose and condensate-pump reservoir every 1 to 3 months with clean warm water or diluted white vinegar.
Wash the dehumidifier’s removable air filter every 2 to 4 weeks so dust does not enter the condensate pan.
Confirm the sump-pump float moves freely from top to bottom without touching the drain hose.
Test your sump basin high-water alarm and battery backup pump if installed.
Inspect the silicone seal or rubber grommet on any radon-mitigation sump cover for cracks.

Because a dehumidifier continues extracting water whenever power is on, a tripped sump-pump breaker can cause the basin to overflow in a finished basement. Pairing your sump pit with a battery-powered water alarm or a battery backup sump pump provides an extra layer of flood protection.

Key Takeaways

Always drain dehumidifier water into the sump basin, never by tapping into the pressurized PVC sump discharge pipe.
Use a garden hose at least 1/2 inch in diameter for gravity drainage so dust and algae do not clog the line.
Keep built-in dehumidifier pump tubing within the manufacturer’s 16-foot lift and length limits, and leave the internal bucket seated if required.
Size external condensate pumps by their actual flow rate at your required vertical lift rather than their zero-flow shutoff head.
Preserve airtight seals and include a water trap or check valve whenever routing a drain line through a radon-mitigation sump lid.

Frequently Asked Questions

Can you hook up a dehumidifier to a sump pump?

Yes, you can connect a dehumidifier to a sump pump system by routing the dehumidifier’s drain hose into the sump basin rather than attaching it to the pump motor itself. The sump pump automatically expels the collected condensate when the water level in the pit raises its float switch. Keep the hose end secured above standing water and clear of the float.

Do I need a condensate pump?

No, you do not need a condensate pump if the sump basin opening is lower than the dehumidifier drain port and the hose can slope downhill continuously. You only need an external condensate pump if the hose route must rise uphill and your dehumidifier does not have a built-in pump.

Can a dehumidifier drain hose go uphill?

No, a standard gravity-drain hose cannot move water uphill; any upward rise traps water and causes the dehumidifier bucket to fill. To pump water uphill—typically up to 16 vertical feet—use a dehumidifier with a built-in drain pump or add an external condensate pump.

Can I connect a dehumidifier drain to the sump pump discharge pipe?

No, you should not tee or tap a dehumidifier drain hose directly into the sump pump’s PVC discharge pipe. Plumbing codes prohibit direct connections to waste or discharge pipes, and high-pressure water from the sump pump can force its way backward up the small tubing and flood your dehumidifier.

How do you connect a dehumidifier to a condensate pump?

Place the condensate pump on a level floor below the dehumidifier and run a short downhill hose from the dehumidifier’s gravity port into a top inlet hole on the pump reservoir. Clamp 3/8-inch ID vinyl tubing onto the pump’s barbed check-valve outlet, route it to the sump basin within the pump’s lift rating, and test the float with clean water.

Can I pass the hose through a sealed sump lid?

Yes, you can route a drain hose through a sealed or radon-mitigation sump lid if you maintain an airtight seal and prevent soil gas backflow. Install a tight rubber grommet or bulkhead fitting sealed with 100% silicone caulk, and add a water-retaining P-trap loop or one-way check valve so radon gas cannot travel up a dry hose.

Will draining a dehumidifier into a sump pump wear out the pump?

No, draining a residential dehumidifier into a sump basin adds negligible wear to a standard sump pump. Even a 50-pint dehumidifier running at full capacity produces only about 6 gallons of water over 24 hours, which triggers just one or two brief sump pump cycles per day.

Conclusion

Routing your dehumidifier drain line into a sump basin gives you hands-free humidity control using a gravity garden hose, your unit’s 16-foot internal pump tubing, or an external condensate pump. Before leaving your setup to run automatically, pour two cups of clean water through the drain path today to confirm steady flow, zero leaks, and full clearance around the sump-pump float switch.

Sources

ENERGY STAR: Dehumidifiers: Continuous dehumidifier drainage options to floor drains or sumps and operating guidance.
U.S. EPA: A Brief Guide to Mold, Moisture and Your Home: Recommended 30% to 50% indoor relative humidity range and moisture-source control.
Frigidaire: Dehumidifier Not Draining: Gravity-hose slope rules, 1/2-inch minimum garden-hose diameter, and line flushing guidance.
GE Appliances: Dehumidifier Draining Options: Built-in pump 16-foot lift and hose limits, bucket seating requirements, and sump basin suitability.
Little Giant: VCMA-20 Condensate Pump: 1/2-gallon tank capacity, 3/8-inch barbed discharge, and flow-versus-lift performance figures.
2024 International Plumbing Code: Section 314.2.1.1 Condensate Discharge: Prohibition against connecting condensate drains directly to plumbing drain, waste, or vent pipes.
U.S. EPA: Radon Mitigation Standards: Airtight sump covers, sealed penetrations, and trapped drain requirements (Sections 14.5.1 and 14.7.4).

dehumidifier setup moisture control sump pump

Daniel Park

Daniel Park covers home air quality for Nordic Design Blog — dehumidifiers, air purifiers, and the replacement filters that keep them working. It is the largest section of the site, and the one readers arrive at with the most specific problems: a basement that never dries out, a bedroom that smells stale, a filter that costs more than the machine did. His guides focus on the numbers that actually predict performance — pint capacity against room size, CADR against square footage, true HEPA against 'HEPA-type' — and on the running costs people only discover after buying. Daniel is more interested in matching capacity to the room than in recommending the largest unit available. He also writes the replacement-filter coverage, comparing original and third-party options on fit, filtration claims, and cost per year. His view is that a dehumidifier or purifier is only as good as the maintenance schedule its owner can realistically keep.

1 Comment

How To Drain A Dehumidifier To The Outside

August 18, 2026 at 8:46 pm

[…] a sump system: see how to connect a dehumidifier to a sump pump before choosing that […]

Reply

How to Connect a Dehumidifier to a Sump Pump Safely

Why Use a Sump Pump With a Dehumidifier