"When installing vanities, I generally make a few reference holes so I can get my bearings in relation to the pipe. I usually get it in 4-6 holes, it doesn’t really matter if you go over though, as it’s the inside of the cabinet. When I’m done I caulk the holes so the rats can’t get through, and then toss a pack of sponges on top! In the end no one is the wiser! "