Water – Persistent sewage smell coming from basement drain


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.

Best Answer

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.