Basement sink issue

[Timmed]

Greetings all. Been trying to troubleshoot an issue with a basement sink for a few years now. The house has a mother-in-law unit in the basement with a full kitchen. There is a utility/laundry room located directly above it in the main house.

The problem is that when I dump a large volume of water into the upstairs utility sink, the kitchen sink below it has water bubble up into it, quite forcefully at times. If I'm just running the utility sink faucet there is no issue, but when the laundry hose drains into the sink it always bubbles up into the basement one. I've snaked the vent and the drain pipe, and neither one solved the problem.

By chance I'm doing demolition in the basement right now and have that wall open, I can finally see what the 1963 drain pipes look like (please see attached pic). The drain is on the left, the vent stack is on the right and goes out the roof. The black ABS stub is where the basement sink was draining. Do you see anything inherently wrong with how this is plumbed? Any ideas on why this would be happening?

Thanks in advance, Tim

p.s. Please ignore the PEX mess, that is all getting cleaned up with the remodel.

 

[James Henry]

The drain is to small.

 

[Sponsor]

 

[John Gayewski]

I bet the vent is clogged and the drains are very likley constricted from years of buildup. Time for some new piping.

 

[Timmed]

The drain is to small

The drains are 1.5" for both upstairs and basement, looks like it transitions to 2" just before it runs under the floor. Isn't that the standard size for drains?

 

[John Gayewski]

The drains are 1.5" for both upstairs and basement, looks like it transitions to 2" just before it runs under the floor. Isn't that the standard size for drains?

Not really. Kitchen sink should be 2"with a 1. 5 inch trap and trap arm.

 

[Jeff H Young]

Everyone is correct , too small , Galvie sucks just what to do? Id recomend trying to tie that w/m into a 3 or 4 inch stack down there if possible and rework from slab up for the basement sink , the gal vent at 4 ft high or around 6 inches above flood rim of sink and put PVC or ABS. or at the least replace everything you can and hope for best