Filled the sink to the brim to soak some dishes as I unplugged the drain I hear water dripping in basement.
No leaking when water is running.
Dry under cabinets so it must be in wall.
I suspected hole rusted in the vent.
Cut open the wall in basement stairwell to check the pipes.
Found the threads at the top of the T to be completely gone. While heavy I could actually lift the galvanized pipe straight up a 1/4in. Repeated test with a full sink and water gushes out from the deteriorated joint.
So my issue Is 2 fold. Drain is partially clogged so that when drain pipe is completely full it backs up to the bad joint which under normal circumstances would just result in slower draining for a few seconds while the drain catches up. But now leaks out.
Super ghetto fix would be to just rod the drain then clean and JB weld the the joint together. In reality this would probably work for a long time.
I'm planning on cutting back the metal pipe near main line and running new pvc from the sink.
The slow draining is caused by a crappy initial plumbing job that has a low spot in the plumbing and actually goes uphill about an inch before going straight horizontal.
I could potentially cut the vent in attic and pull the old pipe up and out of wall. Then drop in new PVC or just cut it just above the T and put a fernco.
