Continuous drain setup: never empty the bucket again

Start with how much water is actually moving

Every decision below gets easier once you know the flow rate, and almost everyone guesses it far too high. A bucket that needs emptying daily feels like a lot of water, so people shop for drainage as though they were plumbing a washing machine.

The arithmetic is short. One US pint is 0.125 gallons, and a dehumidifier’s rating is per day. So an 80-pint machine running flat out all day produces 10.0 gallons in 24 hours — which is 0.42 gallons per hour. Not per minute. Per hour, at maximum, on the one day a year it never stops.

A real basement is undramatic by comparison. For a 1,200 sq ft space that is genuinely wet — beads of moisture on the walls — our sizing function puts the load at 16 pints a day on the modern post-2019 scale (22 on the old one, and it matters which scale a figure is on). That is 2.0 gallons a day, or 0.083 gallons an hour — about ten fluid ounces, roughly a mug of water, in an hour.

Even the 155-pint commercial machine asks under one gallon an hour of its drain. That is the useful finding, and it settles a question people spend a lot of time on: pump capacity is never the constraint. A pump rated 80 GPH is not 192× oversized because it is a good pump; it is sized for air-conditioning condensate, where flows are larger. What does constrain you is vertical lift, hose routing, and whether anything shuts the machine down when the drain path fails. The rest of this page is about those three.

The three routes, honestly

There are only three, and the right one is usually decided by your basement rather than by preference.

Route 1 — gravity, if your geometry allows it

Most portable dehumidifiers have a threaded drain port behind or below the bucket, and most ship with a short hose. Screw it on, run it to a drain, done. It costs nothing, adds no failure points and uses no electricity, and if it works in your space you should stop reading and go do it.

The catch is geometric and it is unforgiving. Water only flows downhill, so the drain has to be lower than the port — and every inch of the run in between has to keep falling. On a portable unit the port sits a few inches off the floor, which means the drain has to be lower than that. In a basement, the floor is usually the lowest thing there is. That is why gravity draining fails so often in exactly the room that needs a dehumidifier most: there is nowhere lower to send the water.

Two workarounds, in order of preference. If there is a floor drain, a sump pit or a sink lower than the port, use it. Otherwise you can raise the dehumidifier — a sturdy shelf, a purpose-made stand, a stack of blocks — until the port clears the drain by enough to keep a continuous fall. Raising it 18 to 24 inches is often the whole project. Be honest about stability: these machines vibrate and hold water, and a 60-pound unit falling off a wobbly stack is worse than a bucket.

If your geometry does work, you do not need to buy anything beyond a hose long enough to reach. We would rather tell you that than sell you a pump you have no use for.

Route 2 — a condensate pump, the usual answer

When there is nothing lower than the drain port, a condensate pump is the standard solution, and it is a genuinely small piece of equipment. Water drains by gravity into a small reservoir; a float rises; the pump switches on and pushes the water up and out through narrow tubing; the float drops and it stops. Cycle over, a few times a day.

The specification that matters is lift, not flow, and pump listings quote both in a way that is easy to misread. Our main pick publishes 80 GPH at 1 foot of lift and a 20 foot shut-off height — the point at which it can no longer push water at all. Flow falls continuously between those two points, so a headline GPH figure without a stated lift is not a working number.

One listing in our data publishes the whole curve, which is worth quoting because it makes the shape concrete: the Aprilaire unit states roughly 120 GPH at about 3.4 feet of lift, falling to roughly 5 GPH at its 22 foot maximum. That is a 24-fold drop across the range — and here is the point: even the worst end of it is about 12 times what an 80-pint dehumidifier can produce. The same listing advises leaving at least 50% headroom over your usage rate. At these flows you will have several thousand percent.

So choose a pump on the height you need to climb plus a sensible margin, not on gallons. Measure from the pump’s reservoir to the discharge point — the vertical rise, not the length of the tubing — and buy something rated well above it.

We earn a commission on purchases made through the Amazon links on this page, at no cost to you. It does not change what we recommend, and every figure above is computed from published specifications you can check yourself.

The one to fit

Little Giant Little Giant VCMA-20ULS 115 Volt, 80 GPH, 1/30 HP Automatic Condensate Removal Pump for HVAC/Refrigeration Sys

80 GPH at 1 ft, 20 ft shut-off, 0.5 gal tank, check valve on the discharge — and an overflow detection switch, which the cheaper model in the same range explicitly does not have.

View on Amazon

$56.04 · 7,601 reviews

Route 3 — a floor drain or sump you already have

If the basement has a floor drain or an open sump pit, you may already own the answer. Run a hose from the drain port and let gravity do the work, exactly as in route one — the pit is below floor level, so the geometry that defeats most basements works in your favour here.

Three cautions. First, if the sump pump discharges beside the foundation, you are lifting water out of the air and putting it straight back into the soil you are trying to dry; make sure the discharge line carries it well away from the house. Second, a hose left dangling into a pit can be pushed out of position or float on the lid, so fix it in place. Third, if you are connecting condensate into household plumbing rather than an open pit, requirements vary by jurisdiction — some places restrict what may enter a sanitary line, and an air gap is normally expected so nothing can siphon back. Check locally rather than taking our word for it; we are not a plumbing authority and will not pretend to be one.

Hose choice, and the failure nobody sees coming

Portable dehumidifier drain ports are usually a garden-hose thread, which means an ordinary 5/8-inch hose fits. Condensate pumps discharge through much narrower tubing — our pick uses a 3/8-inch barbed outlet — because the pump is pushing, so bore matters far less than it would under gravity.

At the flow rates computed above, hose diameter is close to irrelevant. What matters is what the hose is made of and how it lies:

• Use reinforced hose, not soft vinyl. Thin vinyl tubing kinks permanently where it turns a corner or crosses a joist, and a kink is a closed valve.
• Keep the run as short as the layout allows. Every extra foot is more opportunity for a sag, a snag or something being set down on top of it.
• Clamp it at the port. A hose that works loose empties onto the floor silently, which is worse than not draining at all.
• No high points. Anywhere. This is the one that catches people, and it deserves its own paragraph.

Under gravity, a hose must fall continuously for its entire length. Route it up over a step, a pipe or a threshold — even by an inch — and the water reaches that high point, stops, and sits there. Flow does not slow down; it ceases. The same happens at a kink, or where a season of slime has narrowed the bore.

Here is why that failure is so quiet. Plumbing a drain hose does not disable the internal bucket or its float switch. When the hose stops accepting water, the condensate simply carries on into the bucket instead. The bucket fills over a day or two, the float rises, the machine shuts itself off and shows a full-tank light — exactly as if you had never connected a hose at all. There is no leak, no alarm, no puddle. Most people conclude the continuous drain “doesn’t work on this model” and go back to carrying buckets. Nearly always, the real fault is three feet of hose lying an inch too high.

Which gives you a cheap diagnostic worth running once: after setting up a drain, check in two days that the bucket is dry. Not the floor — the bucket. A dry bucket means the hose is carrying everything. Any water in it means the drain path is partly blocked and you have found the problem before it stops the machine.

Freezing, on any run that goes outside

Draining out through a wall is tempting and it is the setup that most often fails in winter. The reason is the flow rate again: at 0.083 gallons an hour, the water in an exterior hose is barely moving and has no warmth of its own. A trickle freezes at temperatures a flowing pipe would shrug off, and once the outlet ices over the run backs up, the water in the line freezes behind it, and you are back to the silent bucket failure — this time with a hose that may split.

If an exterior route is your only option: keep the outdoor section as short and as steeply sloped as you can, never let it end in a low loop where water can stand, and make sure the terminus cannot be blocked by leaves or snow. In a genuinely cold climate, plan to bring the discharge indoors for the winter, or accept that the machine will not drain in a hard freeze.

Worth noting alongside this: most refrigerant dehumidifiers already struggle in cold spaces, since the coil frosts and the machine spends time defrosting instead of removing water. If your crawl space is genuinely cold in winter, the drain is not the only thing you should be checking.

The safety switch, and why the cheaper pump is the wrong saving

A condensate pump is a small motor with a float switch, running unattended in the least visited room in the house. It will eventually fail — a jammed float, a seized impeller, a check valve held open by grit. The question is what happens next.

A pump with an overflow detection switch answers that properly. A second switch sits above the normal float, and when water rises past it, it opens a circuit that shuts the dehumidifier down — no condensate is produced, so the reservoir stops filling. You find a machine that has stopped, which is exactly the outcome you want. It needs to be wired to the appliance, which is basic work but not no work.

The two pumps in our data from the same manufacturer make the trade explicit, and it is the clearest thing on this page. $56.04 buys the 80 GPH model with the overflow switch and a 20 foot shut-off. $47.04 buys the 65 GPH model with a 15 foot shut-off, and its own listing states in capitals that it does not include the overflow detection switch. The difference is $9.00. Whatever your basement contains, it is worth more than that.

Keeping it working

A continuous drain is close to maintenance-free, but not entirely. Condensate is distilled water landing on a coil that has spent the summer collecting dust, and the resulting slime accumulates in reservoirs and narrow tubing. Once a season, flush the pump reservoir and the discharge line with clean water and check that the check valve still seats — a check valve that leaks back lets the same half-litre cycle up and down the tube, which shortens the pump’s life for no benefit.

While you are there, look at the hose run again. Things get moved in basements. A storage box set down on a drain line does exactly what a kink does, and the machine fails the same silent way.

One more sanity check that costs nothing: a dehumidifier which suddenly seems to be producing no water at all is either dry (good — check the humidity reading) or not running (check the bucket, the drain and the float). The distinction is easy to make and easy to leave unmade for a month.

What we cannot tell you

We have never installed any of these pumps, in a crawl space or anywhere else, and no figure on this page comes from a measurement we made. The lift, flow, tank and wattage numbers are the manufacturers’ own published specifications, quoted with the conditions they were published under, because a flow rate without a lift attached is not usable. The water volumes are arithmetic on rated capacity, and rated capacity is a test-condition ceiling — your machine will produce less than the table shows, which only makes the headroom larger.

What we cannot tell you is your geometry: where your drain is, how high your discharge point sits, whether your local code permits a particular connection, and whether the hose you already own kinks at the corner it has to turn. Those are the questions that decide this installation, and they are all answerable with a tape measure in the room itself.

If you want the pump hardware in more depth — sizing, wiring the safety switch, reservoir capacities and how the models differ — that is the condensate pump guide. If you are still deciding what all this will cost to leave running, the running cost guide works through the electricity, and shows why a machine that has been switched off because of a full bucket is the most expensive configuration of all.

Where this leaves you

If nothing in your basement is lower than the drain port

• Published 80 GPH at 1 ft of lift and a 20 ft shut-off — against the 0.42 GPH an 80-pint dehumidifier can actually generate.
• A 0.5 gallon tank and a built-in check valve on the 3/8" discharge.
• An overflow detection switch that can shut the dehumidifier down instead of flooding the floor — the cheaper model in the same range states that it has none.
• At the load worked through above it runs about 2 minutes a day and costs around $0.01 a month to operate.

Buy nothing if you have a floor drain, a sump pit or a sink below the unit's drain port — gravity and a hose are strictly better than a pump, and this page would rather you kept the money.

Little Giant

Little Giant VCMA-20ULS 115 Volt, 80 GPH, 1/30 HP Automatic Condensate Removal Pump for HVAC/Refrigeration Sys

$56.04

View on Amazon

2,000+ bought last month