Floor drain cleaning: what to check before you call a plumber

You’ve noticed it in the basement, laundry room, or garage. There’s a funky smell coming from the floor drain, or maybe a puddle of water that just won’t go away.

So, how the heck do you know if it’s a real clog or just something smelly?

It’s a common call, and most of the time, the fix is simpler than you’d think.

There are really only two things that go wrong with a floor drain. I’ll show you how to tell which one you’ve got and what you can do about it.

What is a floor drain and what does it do?

A floor drain is exactly what it sounds like: a drain set into the floor to carry away water from spills or overflows.

You’ll usually find them in places that might get wet, like utility rooms, basements, and garages.

The most important part you can’t see is the P-trap. It’s a U-shaped bend in the pipe just below the drain grate.

Its job is to hold a small amount of water at all times, and this water acts as a seal, physically blocking sewer gas from coming up the pipe and into your home.

Two common floor drain problems and their symptoms

When a floor drain acts up, it usually points to one of two problems.

The first, and most common, is a dry P-trap.

If a drain isn’t used for a while, the water in that trap evaporates, which usually takes two to four weeks. Once the water is gone, there’s an open path for sewer gas to drift into the room.

The drain isn’t actually clogged, it just smells like something is very wrong.

That trap only blocks gas if it has water sitting in it.

The second problem is a genuine clog from things like hair, lint, and dirt building up in the pipe. If your washing machine drains and water comes up out of the floor drain instead of going down, you’ve got a clog.

That’s a plumbing nightmare.

When it’s just the floor drain backing up, the clog is probably in that drain’s own pipe. If other fixtures like a nearby sink or toilet are also slow, the blockage is likely further down the main drain line that they all share.

How to tell if your floor drain is clogged or just dry

Before you do anything else, run water down the floor drain for a few seconds.

If the smell was your only problem and it goes away after a day or so, your trap was dry. The water you added refilled the seal.

To prevent it from happening again, just pour some water down that drain once a month.

If the water drains slowly or backs up onto the floor, you have a clog.

You can try a few things yourself.

Put on some gloves and remove the drain cover, you might be able to pull out a clump of hair or debris right there.

A wet/dry shop vacuum is also great for sucking out any gunk and standing water in the trap.

How to clear a clogged floor drain yourself

If you’ve cleared the visible debris and the drain is still slow, that can mean the clog is further down the pipe.

A lot of plumbers, myself included, will tell you to skip the chemical drain cleaners.

They often can’t dissolve a real clog, and the chemicals sit in your pipes where they can soften or corrode the joints, especially on older lines.

A small hand snake, or hand auger, can sometimes clear a simple blockage in the trap. You can feed it down the drain to try and break up the clog.

But if a hand snake doesn’t work, that’s where I’d suggest drawing the line for DIY.

The next step involves a much larger, rented drum-style machine and opening a cleanout plug on the drain line itself.

On an older home, that plug can be corroded tight. Forcing it can break the pipe, and when it does come free, it can release a sudden rush of backed-up wastewater.

Here in South San Francisco, with so many homes built in the 1950s and 60s, we run into this a lot.

Those houses often have their original cast iron drain lines.

If you find yourself snaking the same floor drain over and over, the problem might not be what’s going down it, but the old pipe itself. Cast iron can get rough and corroded inside over the decades, making it easy for things to snag and start a new clog.

When that’s the case, just clearing the clog isn’t enough.

If you’re running into a stubborn clog or a recurring problem, give us a call at ASAP Plumbing Pros. We can run a camera down the line to see exactly what’s going on and give you a clear quote for a real drain cleaning solution.

So, if you’ve got a smelly or backed-up floor drain, try adding some water first. If that doesn’t do it and a simple cleaning doesn’t clear the way, don’t hesitate to reach out.

We’re here to help, 24/7.