When you tap a wall, you are creating a small hole in the wall so that moisture can escape. This term is used when you want to know if there is moisture trapped inside the walls of your home. The tapping process involves using a hammer and chisel or special wires with sharp ends to make small holes in the drywall.
Tapping is also used as an inspection tool by plumbers and electricians because it allows them to see what’s behind the walls without having to tear down part of the structure.