We remodeled a basement bathroom about a year ago and had all of the cast iron plumbing replaced with PVC (by a plumber). I have hooked up the toilet and bathtub which drain great. I then hooked up the sink, turned on the water and it immediately backed up into the sink. I tried a snake the drain and it stops and feels like I hit something hard before the stack. I also tried to vacuum and blow the line and there is no air movement.

I am about 90% sure a plastic knockout cap was left in one of the fittings near the stack.

Question:

Do I cut the drywall out then cut the PVC pipe to remove the cap?
Or do I use a drain snake with a cutting tool to chew it up? The drain goes from 1 1/2" to 2" to 4" down the line so if I chew it up it may flush onward.

i can't imagine that a real plumber would plug a pipe inside the wall and then glue an elbow over it for a stub out..
if you try to chew it up with a cutting tool, you will leave sharp edges for hair to hang up on. you will never get it smooth.
open it up and find the problem..

I normally use a cleanout tee and a rubber test ball to seal the pipe for an air test. I don't suppose there's a cleanout tee visible in your situation ?

get you an inexpensive scope to look down the drain to check Look on a major auction website or a major internet shopping site and search for "endoscope" get one for android for about $15-20 buck to look using your galaxy cell phone...



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Remove the trap and look into the pipe. If the test cap is still there you will see it, but HOW you remove it will depend on how the trap is connected. You have to take it out, not push it into the drain line.

I believe this knockout cap was installed into the elbow that attaches to the main drain/vent pipe. This is about three feet from the sink drain. I will try the scope to verify this it looks like the USB ones are cheap. One of the issues here is that the project was done in two phases with two different plumbers. I will accept some of the responsibility on this one for not looking for a cap. It looks like the best option is cutting drywall and pipe if the plug was left inside.

Thanks for the replies.



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