Sorry for the dumb question but I don't understand something. I constantly read that plumbing pipes should not be placed in exterior walls but rather located inside the conditioned space. Why are there so many kitchen sinks under exterior windows? Are the supply lines kept inside the wall and hidden in the cabinet? Can the DWV be kept out of the exterior wall too? Is the Ptrap really the only place water could freeze and that should be under the cabinet? I'm doing a design and this has always perplexed me.