Originally Posted by Alan
If you do this and the drain is still clogged you'll end up flooding underneath your cabinet, so be careful......
Good point...didn't think of that....but that would also lead me to believe that maybe that is the problem. Being so close to the drain, gunk has got into the check valve and is preventing it from opening.
I use something similar in my regular job...but we call them vacuum breaks. We also put them up fairly high to keep the hot water away from them (they can be subjected to steam on a regular basis)