I'm not sure the formal name but I walked into an RV dealer and told the man "I need a hat for the Stink Pipe" and ... He took me directly to it, no ambugity at all, he led me directly to the display..
Suggestion.. Consider one of the advanced units like the RV 360 sanitation vent
Click here for a page of them on AmazonI use a different advanced model on the black tank.. These look,,, interesting though.