The standpipe is the vertical pipe behind a washer that the drain hose drops into. It's one of the least glamorous parts of a laundry setup, and one of the most common sources of water on the floor. Many symptoms that look like a washer problem, including leaks, slow cycles, odd noises and smells, start here.
Below we go symptom by symptom, explain what's happening and suggest what to check.
How a standpipe is supposed to work
When the washer pumps out, water flows up and out the drain hose, then falls into the standpipe, which carries it through a trap to the house drain. Two heights matter:
- •The top of the standpipe has to be high enough that the washer's water level doesn't siphon out through the hose when the washer is filling or sitting idle.
- •The highest point the hose reaches can't be so high that the washer's pump can't lift water over it.
Manufacturers give their own limits. LG's top-load washer instructions, for example, say not to install the end of the drain hose higher than 96 inches above the bottom of the washer and to attach the elbow bracket within 4 inches of the hose end. Most installation manuals also give a minimum standpipe height; check yours, since requirements vary between brands and between front-load and top-load models.
Symptom: the washer drains while it's filling
You notice the washer fills for a long time, the tub never seems to reach its level, or you can hear water trickling into the drain during the fill. The washer is siphoning: water is flowing out of the tub through the drain hose by gravity.
Common causes: - The standpipe or the hose's high point is too low, below the washer's water level. - The drain hose is pushed too far down into the standpipe, forming an airtight seal that encourages siphoning. - The hose has been extended or replaced with one that doesn't hold a proper hook shape.
What to check: Pull the hose up so only a few inches go into the standpipe, secure it with the elbow bracket, and make sure there's an air space around the hose. If the standpipe itself is very short, a plumber can tell you whether it can be extended.
Symptom: water overflows the top of the standpipe
The floor is wet behind the washer after a drain cycle, and the top of the standpipe has water or lint residue around it.
Common causes: - A partially clogged drain line or trap. Lint, detergent residue and small items build up over time. - A standpipe that's too short or too narrow for the washer's pump rate. - A drain shared with a laundry sink that's backing up. - The hose sealed into the pipe, preventing air from escaping.
What to check: Watch the standpipe during a drain cycle. If water rises and nearly overflows, the drain beyond the standpipe is restricted. Clearing the trap and line is plumbing work; a plumber with an auger can do it. If the standpipe drains fine but the floor is still wet, check the drain hose for cracks and the washer for leaks.
Symptom: sewer gas smell in the laundry area
Common causes: - A dry trap, if the standpipe is rarely used. - A trap missing or improperly configured. - The hose sealed into the pipe so that air pressure pulls water out of the trap.
What to check: Run water into the standpipe to refill the trap. If the smell persists, have a plumber inspect the drain.
Symptom: the washer pumps slowly or shows drain errors
Common causes: - The drain hose's high point is too high for the pump. - The hose is kinked behind the washer. - The washer's pump filter or the pump itself is clogged.
What to check: Pull the washer out and inspect the hose route. Most front-load washers have a pump filter behind a small access panel at the front bottom; clean it. Our guide to front-load washer floor requirements covers moving the machine without damaging hoses.
Basement laundry in older homes
Many older twins, colonials and brick rows in the region have laundry in the basement, and the washer often drains into a laundry tub rather than a standpipe, or into a standpipe that drains to a pump if the main drain is above the basement floor. Those setups introduce their own issues:
- •A laundry tub drain clogged with lint backs up into the tub and over the edge.
- •A sump or ejector pump that can't keep up with the washer's discharge rate.
- •An older drain line, sometimes cast iron or terra cotta, that's partly blocked.
If your washer drains to a tub, a lint trap on the hose end helps. If it drains to a pump, the pump's capacity should be checked by a plumber.
In new-construction homes with laundry on upper floors, the standpipe is usually built into a recessed wall box. Those boxes can be tight, and the hose is often jammed too far into the drain to make it fit, which brings the siphoning problem above.
Don't seal the hose into the pipe
It's tempting to tape or caulk the drain hose into the standpipe to stop splashing. That creates an airtight connection that can siphon water from the washer and pull water from the trap. Leave an air gap around the hose.
Code questions
Standpipe height, diameter and trap requirements are set by plumbing code, and they vary. If you're installing a new standpipe or relocating a laundry, consult a licensed plumber or your township or borough code office (in Pennsylvania) or your town's construction official (in New Jersey).
When to call a technician
If you've corrected the hose and standpipe setup and the washer still drains slowly, siphons, shows drain error codes or leaks, the problem may be in the washer itself: the pump, pump filter, a check valve or a pressure sensor. Our washer repair technicians can diagnose it. Book a visit online and describe the symptom, including whether your washer drains to a standpipe or a tub.