Last Updated on October 26, 2026 by Umar Farooq
A laundry floor drain is the only thing in the room that limits how much damage a failed hose does. A washing machine supply hose holds around 70 pounds of pressure and puts out roughly 650 gallons an hour when it lets go — a 2-inch floor drain swallows that comfortably, and a sheet of vinyl flooring does not. So the answer to “should I cover it” is: put a grate on it, never a cap, and fix whatever made you want to seal it.
Almost nobody arrives at this question out of curiosity. They arrive because the drain smells, or because water came up out of it, or because the cast-iron grate has rusted into lace and there is now a hole in the floor. All three have fixes. None of the fixes is a plug.
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A capped drain is protection you believe you have
This is the part worth sitting with, because it is the one that costs money later.
A laundry room with no floor drain is a room where you know you have no margin. You check the hoses, you close the taps when you travel, you keep an eye on the pan. A laundry room with a drain that has been capped, grouted over, tiled across or hidden under laminate is a room where you believe there is a margin and there is not — and the belief is what changes your behaviour. The flood that follows is the same flood, arriving at a floor nobody was watching.
State Farm paid out nearly $30 million on hose-failure claims in a single year. At 650 gallons an hour, a weekend away is about 31,000 gallons. The drain is not a nice-to-have in that arithmetic; it is the difference between a wet floor and a ceiling coming down. If your laundry is upstairs, the whole calculation is different again and we have set it out at second floor laundry leak protection.
The smell is a dry trap, not a drain fault
Under the grate there is a U-bend holding a few inches of water, and that water is the only thing between your laundry room and the sewer. It is called a trap seal, and in a drain nobody uses it evaporates.
Two things in a laundry room make this worse than anywhere else in the house. The drain gets used approximately never — it exists for an emergency, so months pass with nothing going down it. And an electric dryer vented outside pulls air out of the room continuously, which drops the room pressure slightly and gives sewer gas a reason to come up through a trap that no longer has a seal in it.
The free fix, which works and costs nothing: pour a bucket of water down it. Do that every month or two and the smell does not come back. If you want it to last longer, float a cup of mineral oil on top of the water — oil evaporates far more slowly, so the seal survives a longer gap. That is the whole repair, and most readers can stop here.
The reason a product exists at all is that remembering is the weak link, and the plumbing codes agree — they require trap seal protection on floor drains precisely because nobody remembers. A trap primer tees into a nearby fixture’s waste and drops a small amount of water into the floor drain’s trap every time that fixture is used. In a laundry room that fixture is usually the tub, which is convenient, because the tub gets used.
Water coming up is the opposite problem
If the drain is pushing water out rather than taking it in, nothing above applies. A dry trap lets gas up; a surcharged drain lets water up, and the cause is downstream of you.
It means the line the floor drain discharges into cannot accept what is arriving. Sometimes that is a partial blockage in your own branch, in which case rodding it clears it. Sometimes it is the municipal main backing up during heavy rain, in which case the floor drain is simply the lowest opening in the building and water is finding the lowest opening it can. That second case is the one a backwater valve is for, and it is also the one that makes people cap the drain — which converts the lowest opening in the building from a drain into a pipe that is still connected to the sewer and now has a lid on it.
If the water coming up smells of detergent rather than sewage, suspect the washer’s own discharge first: a pump moving 15 to 20 gallons a minute into a restricted branch will surface at the nearest opening. That diagnosis belongs on washer backing up into sink and how to stop a washing machine flood.
Measure the laundry floor drain opening, not the pipe
This is where orders go wrong, and the mistake is understandable. Floor drains are specified by the outlet pipe they connect to — 2-inch, 3-inch, 4-inch. The grate is a different number entirely, and it is the one you need.
Take three measurements before opening any listing. Across the opening, at the rim the grate sits in, in inches to the nearest eighth. The depth of the recess, because a grate thicker than the rebate stands proud and becomes a trip hazard. And how the existing one is held — two screws into the drain body, a snap-in friction fit, or simply dropped in. Replacements are sold by grate diameter and by attachment type, and they are not interchangeable.
While the grate is out, look down. If you can see standing water a few inches below, your trap is sealed and healthy. If you can see dry pipe, you have just found your smell.
One part each for the smell, the backup and the grate
Three different failures, three different parts. Nobody needs all three.
Zurn Z1021WL-PC trap primer: for the drain that smells every August
This is the fix for a trap that keeps drying out in a laundry room that already has a tub. It is a chrome-plated cast brass body with a cleanout and a ground-joint elbow with a 1-1/2-inch NPT outlet, and it ships with a reducing washer for a 1-1/4-inch sink tailpiece and a stainless braided primer hose with 1/2-inch compression fittings. It fits into the tub’s waste, so every time the tub drains it sends a measured shot of water to the floor drain’s trap.
Who it suits: a laundry room with a sink or tub within reach of the floor drain, and a drain whose smell comes back no matter how many buckets you pour. Our laundry tub sink page covers the tub side of that connection.
What it does not do: it will not help a laundry room with no fixture to tee off, and it does nothing at all for water coming up. It also needs the primer line run to the drain body, which on a finished slab means either an accessible route or a chase.
RectorSeal Clean Check 97024: for the drain that floods in heavy rain
A 4-inch extendable PVC backwater valve with an in-ground flapper, designed to sit in the sewer lateral outside and to be serviced from above ground rather than through an indoor access pit. RectorSeal’s stated application is exactly the problem described above — preventing sewage backup caused by a plugged sewer, excess volume in the system, or groundwater flooding — and it installs up to 12 feet below grade without a manhole.
Who it suits: a basement laundry that has actually backed up, more than once, during storms. If that has happened, this is the part that addresses it and the cap does not.
What it does not do: this is not a Saturday. It goes in the lateral, which means excavation, usually a permit, and a plumber. It is on this page because it is the correct answer to the second failure mode, not because it is an easy purchase. Availability on this listing is thin, so check before you plan around it.
Zurn Wilkins ZN400-5B strainer: for the grate that has rusted away
A polished nickel-bronze round strainer top from Zurn’s ZN400 series — the replacement for an original cast-iron grate that has corroded through, which in a damp basement laundry is a matter of time rather than bad luck. Nickel bronze does not rust, and the open area is designed for drainage rather than decoration, which matters when the thing it is there for is a burst hose.
Who it suits: a drain whose grate is broken, missing, or so corroded it no longer sits flat. A flat, solid grate also ends the temptation to put a rug over the hole.
What it does not do: check your measurement first. This is the 5-inch top. The ZN400 series is sold in several diameters and they do not interchange, so measure across your opening before ordering, and confirm whether yours is a screw-down or a drop-in top.
When buying nothing is the right answer
If your drain is clean, the grate is sound and the smell goes away when you pour water down it, buy nothing. Put a reminder in your phone for the first of every other month and you have solved it.
If you have no floor drain at all, do not start here. Cutting a drain into an existing slab is a large job with a poor return compared to a washing machine drain pan plumbed to a nearby waste, or to a sealed floor that contains water rather than removing it — which is the approach on waterproofing a laundry room floor.
And if the drain backs up every single wash rather than during storms, the backwater valve is the wrong part. That is a restriction in your own branch, and it wants rodding and a camera, not a check valve holding the water in.
FAQ
Can I cover a laundry floor drain with a rug or a mat?
Not with anything that holds water against the floor or hides the grate. A mat over a drain stops you seeing the first inch of a leak, which is the inch where you still have options. If the drain is unsightly, a flat replacement grate in a corrosion-resistant metal is the answer.
Why does my laundry floor drain smell only sometimes?
Because evaporation is seasonal. A trap loses its seal faster in dry heated air, and the dryer running pulls room air out and makes gas more likely to be drawn up. A smell that comes and goes with the weather is a trap seal, not a blockage.
Is it legal to seal off a floor drain?
Capping an active drain is a plumbing alteration, and in most jurisdictions an abandoned drain has to be properly disconnected and the opening made part of the floor — not plugged and forgotten. Check locally before you do anything permanent, because a capped-but-connected drain is the version that causes problems.
Will a floor drain handle a burst washing machine hose?
A 2-inch floor drain handles several hundred gallons an hour, which is more than a single supply hose can deliver. What limits it is not the drain — it is whether the floor actually slopes toward it. Pour a jug of water in the middle of the room and watch where it goes.
Does a trap primer need power?
No. The type on this page is mechanical and runs off the water flowing through the fixture it tees into, so there is nothing to plug in and nothing to fail electrically. Other types sense supply pressure instead; both are passive.
Pour a bucket down it this week
The order worth following: lift the grate, look down, and see whether there is water in the trap. If there is not, that is your smell and a bucket fixes it today. If the grate is corroded, measure the opening across the rim and replace it with something that will not rust. If water has come up out of the drain during rain, that is a different problem and a valve in the lateral is the part that addresses it.
What not to do is the easy thing. A cap makes the symptom go away and takes the drain with it, and you will not think about that again until the night a hose lets go and 650 gallons an hour arrives on a floor you thought had somewhere to put it.
