Mud daubers "Duh"

We live with the little buggers too. They are busy bugs! There are small screens that come in a set of three sizes available at camping world and other hardware stores that are made for drains. I use the smallest in my sink but the largest one fits perfectly in the roof vents for sinks and potty. Just remove the cap, glue it in and replace the cap to prevent them and regular wasps from stopping up those vents as well because they will get in there. Had to clear our new/old camper of them when we bought it and it was being used. Drains work much better after that fix. Had some tiny kind of bug that plugged up our umbilical plug from truck in just two days in Michigan being left unplugged while on shore power. Taping ends only solution for that.