I've recently purchased a house and am now learning all the ins and outs of home maintenance. This summer, I've noticed that I have a very smelly basement drain. Particularly, it smells like sewage.

I figured that this wasn't a problem, in that the majority of things I've read state that it simply needs to have water poured in (with or without Mr. Clean) to replace the dried out water in the trap.

This worked fine last year, however this year the smell is back, and far worse. Now, I am essentially pouring water down the pipe every other day to flush the smell. The problem, however, is that it is also ridiculously hot where I am, so we have to run the A/C quite often. As the drain stinks up the basement, that lovely smell gets pulled into the A/C ducts in the basement and then vented throughout the house.

My question is....is this common for this sort of drain? I can't really get my hand into the pipe itself (probably about 3in in diameter), so I can't really see if there is a plug that needs to be checked. I hesitate to call a plumber if it is trivial, but the persistent poo smell is starting to drive us nuts.


My wife and I went through the house, flushing toilets and watching the water in the drains. Not a ripple for any flushes.

Second edit

Flushed down some Mr. Clean / water mixture and, while it kept the smell at bay for a few days, it is starting to come back. I believe that a plumber is definitely in our future, as I've exhausted the helpful advice provided.

  • I think longnecks answer covers the likely cause, but also consider you could have more than 1 drain, or maybe a toilet rough in that isn't covered, etc. Check the cover on your cleanouts.
    – Steven
    Jul 15, 2014 at 2:11

2 Answers 2


You are correct that floor drains do need to be monitored and occasionally the trap refilled with water.

So the first thing to check is that your floor drain actually has a trap. The way to do that is to slowly pour water in to the drain. You should notice the water level rise and stay there. If the water disappears quickly then it's likely you don't have a trap.

Provided that the drain does have a trap, the next thing to figure out is why the trap is emptying so quickly. A common cause is something wrong with your vent stack. Problems can range from a blockage, to an improperly vented drain elsewhere, to no venting at all.

A good way to test your vent stack is to flush each toilet one at a time. Enlist a helper and keep an eye on the water in the trap. If one toilet causes the water in the trap to move significantly or drain completely, you have found your problem fixture or vent stack. Fixing this could be as simple as running a garden hose up to your roof and down that vent stack to clear the blockage.

If climbing on the roof is not for you, then a standard house-call charge from a plumber will likely fix it, and that's not usually too expensive.

But if a fixture is incorrectly plumbed or inadequately vented, that can get pricey.

  • If the house has set vacant for a while before you purchased it, most likely the water evaporated, allowing the smell to pass through. Old homes tied these drains to the sewer, that is no longer code. Longneck is correct on the other scenarios, but the chances are the trap just dried up.
    – Jack
    Jul 14, 2014 at 3:18
  • We moved in immediately after the previous owners moved out. When I pour water in it pretty much remains at the same level...I'll give the toilet thing a try.
    – erik
    Jul 14, 2014 at 3:57
  • Updated the post...no water movement in the drains when toilets were flushed.
    – erik
    Jul 14, 2014 at 22:44
  • If it was a trap drying out, one trick is to pour a bit of e.g. olive oil into the drain, so it forms a thin layer to block or reduce evaporation. Apr 3 at 20:47

My friend had a persistent sewer smell in the basement -- and it became so bad that it permeated the whole house to the point that she couldn't live there. This was in late summer of 2016. She had at least three plumbers (supposedly experts) who checked the vents, connections etc. A rooter company did their thing -- the gas company checked and the fire truck came out when she said she had a gas smell. They used their sniffers, yielding no results and no answers. An engineer from the utilities district also checked and implied that she was "smelling things" since he couldn't smell much of anything.

Somehow she found an older plumber who looked at it and said that the cast iron trap in the sewer line looked like the original when the house was built some 70 years ago. The sewer trap was probably leaking under the floor and since the concrete is porous the smell was coming up under a wide portion of the basement floor which was wet underneath. He replaced the trap and found the old one was leaking and it was wet and muddy (and smelly). He said it would take quite awhile for the smell to go away. We put in an exhaust fan and a hose and exhausted the air out of a basement window. It took about 6 months to get rid of the smell.

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