The switch on the wall was wet? What kind of plumbing takes water over to that area?

After I moved in and did work on the house I had a leak problem under my kitchen sink, to the point that the MDF in the bottom of the under-sink cabinet swelled and buckled and got moldy. I finally broke it up and pulled it out and had nothing under there. When I finally called a plumber he looked at the odd mix of pre-cut PVC that was stuck together to drain from the sink to the wall - "the carpenter put it in" (when the sink was put in the new countertop). He understood enough and went to work, removing the various twists and turns and leaving with a tidy descending line with the trap bend and nothing more. It was later when an English professor friend was visiting that I had help to put a new piece of MDF under the sink. :)

SRS