My water tank vent empties into the galley sink. My old boat vent emptied
into the shower stall. I like this arrangement because it does not let in
salt water and we can just watch the sink for an indication as to when the
tank is full.

Neither of those locations is the best place for a water tank vent.
They're both full of bacteria and can also become clogged--in a sump by
soap scum, hair etc...in the galley sink by grease, food particles etc.
Plus, if the sump pump fails or the galley drain gets plugged, shower or
galley water can back up into the vent and even the tank.

Out a through-hull is the best place for a water tank vent...into the
bilge a VERY poor second. At least both of those locations allow you to
flush out the vent by overflowing the tank out it each time you fill it.

--
Peggie
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Peggie Hall
Specializing in marine sanitation since 1987
Author "Get Rid of Boat Odors - A Guide To Marine Sanitation Systems and
Other Sources of Aggravation and Odor"
http://69.20.93.241/store/customer/p...40&cat=&page=1