Pipes, gas lines and electrical cables that enter your property often have gaps around them that have been haphazardly filled with some kind of caulk. But the caulk eventually cracks, peels and falls off. These gaps let in outside air, plus they are ideal entry points for mice and insects. Seal gaps with expanding foam. For water pipes under the sink, unscrew and pull back the escutcheon ring, then caulk around the pipe. The ring is just decorative, you'll be surprised how big a hole there is behind.