Sewer-ish smell in basement kitchen

[slevans]

My home is a two-family, so there is a kitchen in the basement. When a large amount of water is dumped down the first floor kitchen sink, it backs up into the basement kitchen sink.

But not always. Only sometimes. Can't figure out why it happens when it does, and why it doesn't when it doesn't.

Meanwhile, there is a constant sewer-like smell in that basement kitchen.

I had a drain guy come out and he snaked the basement kitchen drain and replaced the caps on the trap located nearby in the basement floor. The smell went away for a while, but then it came back. He came back and did it again, and the smell went away for a while. But now it's back. Again.

He says the smell is not a sewer smell. But it's not a normal basement smell either, and it's coming from that basement kitchen sink.

What could be causing this? It's not dry traps, because we checked that.

Thank you for your ideas!

 

[Terry]

The upstairs sink drains below the downstairs sink. The downstairs vent can tie in at 42" above the next floor up.
Dropping a load of washer can siphon a trap in the venting isn't correct.

 

[Sponsor]

 

[WorthFlorida]

The next time you have the smell, close the drain with the drain stopper and put a little water in the bottom of the sink to sort-of-seal the drain. If the smell goes away and doesn't return after a few days or when it usually occurs, there is the source of your problem.

As Terry suggest it seems like venting is not proper. As a column of water rushes down the drain pipe (waste stack) from upstairs, it creates vacuum behind it and it pulls air from the vent above it. If the vent is not large enough or with some obstruction, it will suck water out of a trap along the way and air then comes from that drain or sink. This is usually where the source of the sewer gas smell comes from. After the trap is filled up with water the odor will stop. I'm guessing that the basement sink is wet vented. A solution might be to install at the basement sink an AAV (Air Admittance Valve).

If you really sure it is not a dry trap problem, pour some bleach down the drain and let it sit there a few hours before rinsing. Maybe, when the drain backed up to this sink, residue or just old slim is lining the pipe at the drain from many years of use or no use.

 

[slevans]

Thank you everyone! This theory makes a lot of sense and I think you're right. If the venting wasn't done correctly, it would be consistent with a lot of other things that weren't done right by previous owners!

 

[Reach4]

I had a drain guy come out and he snaked the basement kitchen drain and replaced the caps on the trap located nearby in the basement floor.

How big was the cutter on the snake? Was it a big power unit?

Did he comment on what the cutter showed? I think this is probably mainly a clogging problem where the pipe turns from vertical to horizontal. Yes, the venting is probably not right, but I think the backing up into the downstairs sink is not a vent problem.

Would your cleanout be suitable for pushing a brasscraft drain bladder down into?