I'll bet that every time somebody mentions vent filters, Peggy goes outside and yells at the moon or kicks her cat?
Understand the process! With sufficient oxygen, poop doesn't smell.
With insufficient oxygen, it goes anaerobic and it stinks, strong enough to clear out an anchorage.
Get sufficient oxygen into your tank, no STINK. Single 1/2" or 3/4" vents that wend their way through the boat are insufficient. Then, because the poop STINKS, you put a filter on the line? Filtering makes the situation worse.
Install 2 - 1.5" vents or an air pump such that you get tons of oxygen into the tank. No more STINK.
You can stop buying useless, expensive poop vent filters every 6 months and donate the money to a home for bankrupt poop-filter makers.