Plumbing Questions? Ask a Plumber and Get Answers ASAP.
Hi may name is ***** ***** I have been in the plumbing field for 20 years. I will be glad to help you today. Is this an older home? Do you have a basement, slab or crawlspace? Are you on city sewer or septic?
IF you remove the studor vent does it still back up? click here
Does the drain pipe go into the floor or the wall? Is there a window over the kitchen sink?
Has it always drained slow or is it a new issue? Is there one pipe or two going into the wall?
If you hook the lower drain pipe to a sink but leave the higher one unhooked, does that sink drain well like that? Place something to catch water if it does not.
How would it drain into the other sink if it were unhooked?
So, to be clear, when you leave the higher pipe in the wall unhooked and hook the lower pipe to a sink it does not back up at all like it was when you have them both hooked up?
The vent may be clogged and most would say that the vent from the roof, but really it is more likely that the vent is horizontal in the attic and a strap came loose. That will cause a belly in the pipe. Rain water will get into it and fill that belly with water and stop up the vent. Some of that water may have come out and got the vent working or it very well may be clogged with debris where it exits the roof. Check for a sagging vent pipe in your attic and strap it up. It is very likely to be the cause of the issue.
Leaving the higher sink open was a temporary vent and that is why that worked then. Once both sinks are hooked up again and the traps are filled with water again then the issue will return.