I don't do it in my coach as generally speaking it is a closed system except for the roof vents.
However, when I leave my Florida house for the summer season I block off all of the sinks and put RV Fresh Water Antifreeze in the toilets along with a small amount of cooling oil on the surface to reduce evaporation.
I also stuff a rag into the clothes washer drain stand pipe.
While living at the house we have had large roaches (palmetto bugs to Floridians) come up through the drains while using the sinks. Scared the hell out of my wife one day while she was brushing her teeth.
Dr4Film ----- Richard
2002 Monaco Windsor PBT 40Ft. (R HOME) - 30Ft. 2006 Pace Trailer (R JUNK). Trailer Has 06 VUE (R TOWD) 04 Victory Alen Ness Edition (R RYDE). Full-Timer for 14 Yr's BUT now a Part-Timer. Cummins ISC-350 With Banks Power Pack and Upgraded PRXB PacBrake.
We are at our Winter Home in Flagler Beach FL