I'm replacing the cabinets in the guest bathroom and have a question about plumbing for the sinks. The new cabinets are 3" taller than the older ones and the new sinks that are being installed are only 4" deep. To take advantage of the gain in under cabinet space, I need to move the existing plumbing within the walls up. The house is 25 years old and I suspect that over the years, some settling has already changed the pitch of the plumbing, resulting in many clogged drains (fill with some type of sediment goop). What is the optimal pitch of the plumbing from the sink drain (after the p-trap, within the wall) to the main pipes?
I'd love to fix this during the tear-out, take care of all of the drywall at one time, thanks for any help.