Have seen this before and never been able to figure out what it is. Don’t see it all the time, but occasionally. It is a small plastic, presumably pvc, pipe sticking out of an exterior wall. It is NOt the water heater pan drain, TPR drain, A/C condensate drain. It was located on a dining room wall. Closest plumbing type stuff was probably 20’ away further to the left in the picture.
What the heck is it?