Why does it only smell at night?
In our case it was the built up gook in the sink drain. During the day there is a lot of movement, window open, and generally things going on. At night things calm down and that odor from sink drain builds up. I tried to figure it out forever but luckily was brushing my teeth one day and turned on water, the water displaced that odor in once whiff which I smelled. I knew that was the smell so bought some of those drain sanitize rods you just drop down in the drain. They last several month according to label. Even with door closed at night no more odor.
