Skip to content

Emergency repairs 24/7 Booked jobs Mon to Sun, 8AM to 8PM

A floor drain with a trap, and why the CR still smells

A trap is a little water sitting between your bathroom and the waste pipe. Keep the water there and the smell stays in the pipe. Lose it and the pipe breathes into the room, however often you scrub the tiles.

Most of the time the fix is a pail of water. If it is not, and the smell comes from a pipe or a vent, that is part of our drain and toilet declogging service. Check which trap you have first.

Send the problem Drain work

Which trap do you have?

Where a floor drain blocks A floor drain in cut-away. At the top, the grate set into the floor. Directly under it, a mat of hair and soap, within reach of a hand. Below that, the pipe drops into a trap holding its water seal, with sand and grit settled at the bottom of the bend. From the trap, the pipe runs away toward the sewer. The blockages sit at three depths, and the article's steps work down through them in order. the grate lifts out the hair mat, just under it the water seal in the trap grit settles at the bottom past here is the snake's job

Drag the drawing sideways to see all of it.

A floor drain in section. The grate lifts out, hair and soap mat just under it, and below that the trap holds the water seal that keeps the smell of the line out of the CR. Grit settles at the bottom of the trap.

Lift the grate off the floor drain and look down.

A cup with a cover sitting in it

This is a bell trap, the type built into most cheap floor drains here. Water collects in the cup and the cover dips into it, which makes the seal. The seal is shallow, so it dries out quickly in a drain nobody uses, and hair and soap fill the cup fast. Some floor drains sold as "anti-odor" use a small flap or float in place of the cup.

A straight pipe going down

Either the trap is a bend in the pipe under the floor, a P-trap, or there is no trap at all. A P-trap holds more water and lasts longer between uses. You cannot see it, so the pail test below is how you check it.

An empty hole where a cup used to be

Someone took the cup out, usually to make the floor drain faster in a wet shower area. The drain empties quicker and the smell comes straight up. Put a cup back in, or replace the drain body with one that has its trap built in.

The pail test

  1. Pour a full pail of water slowly into the floor drain.
  2. Leave it for a day without using the drain.
  3. The smell is gone: the trap had dried out. Pour water into that drain every week or two, or add a spoonful of mineral oil or unscented baby oil after the water so it floats on top and the water evaporates more slowly. Not cooking oil, which sets in the pipe.
  4. The smell is back within hours: the water is leaving the trap, or the smell is not coming through the trap at all. Read the next part.

When water does not fix it

  • The trap gets sucked dry. If you hear the floor drain gurgle when the toilet is flushed, the vent may be blocked. Air is pulled through the trap and takes the water with it.
  • A crack or an open joint under the floor. The trap is fine but the pipe around it leaks gas. Often the smell is strongest along a wall or near the toilet base.
  • The septic tank. A strong smell from several drains at once, worse after rain, can be a full tank. See septic tank trouble.
  • Water coming up, not just smell. A floor drain that fills from below in heavy rain is a different problem, covered on our backwater valve page.

Choosing a floor drain during a renovation

A shower's pace beside a washing machine's The same floor drain drawn twice. On the left, a shower: water arrives gently, the drain takes it as it comes, and the pipe below runs clear. On the right, a washing machine emptying: the pump pushes the whole drum out in a couple of minutes, water backs up in a ring around the same grate, and below the grate lint is matting in the pipe at the point where the flow slows. A shower's pace arrives slowly floor drain the drain keeps up The machine's pace pumped out fast backs up here lint mats here where the flow slows

Drag the drawing sideways to see all of it.

The same floor drain under a shower and under a washing machine. A shower arrives at a pace the drain can take; a machine dumps its load at once, which is worth knowing before you pick the drain for a laundry area.

If the floor is coming up anyway, it is the cheapest time to get this right. Ask for a floor drain with its trap built in, or a P-trap under it, and make sure the cup or insert can be lifted out for cleaning without tools. In a spare CR that will sit unused for weeks, a deeper seal matters more than a fast drain. Our guide to rough-in plumbing covers what to check before the tiles go down.

Questions about floor drain traps

Should a floor drain have a trap?

Yes. Any drain that connects to the waste line needs a water seal between the room and the pipe, or the smell from the pipe comes straight up into the room. The trap can be a bend in the pipe under the floor or a cup built into the drain itself.

Why does my CR smell even though it is clean?

Most often because the trap has dried out. A floor drain in a CR nobody showers in, or a spare bathroom upstairs, gets no water for weeks, the seal evaporates, and the pipe breathes into the room. Pour a pail of water in and wait a day.

What is the cup under my floor drain grate for?

It is the trap. Many floor drains sold here have a small cup under the grate with a cover that dips into it. Water sitting in that cup is what blocks the smell. Take the cup out to make the drain faster and the smell comes straight up.

Is a P-trap better than the cup type?

It holds more water, so it dries out more slowly and clogs less. The cup type is easier to clean because you can lift it out. Changing from one to the other means opening the floor, so it is usually done during a renovation.

The smell is there even after I pour water in. Now what?

Then the seal is not the problem. It can be a cracked pipe under the floor, a joint that was never sealed, or a vent that is blocked so the trap gets sucked dry every time the toilet is flushed. That needs someone to look.

Still smells? Send us the detail

Four things and we can get back to you. The more you put here, the less there is to work out when we do.

We ring or message you back on this number. Nothing else is sent to it.

We reply here in writing, and use it for nothing else.

Your town or barangay helps us send whoever is nearest.

If you would rather chat

A written message reaches us with the detail already in it, so we know what is wrong before we ring you back. For a quick question first, the chat button sits in the corner of every page.

Monday to Sunday, 8AM–8PM
Emergency Repairs Available 24/7

Smell that will not go away?

Traps, vents and the pipes under the floor are part of our drain and toilet declogging service. Send us the problem and say what the pail test showed.

Emergency repairs 24/7 Booked jobs Mon to Sun, 8AM to 8PM

Send the problem Drain and toilet declogging
Send the problem Chat
Message us

Message us

Ask about a job, an area or what something costs. We reply by email or ring you back.