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Old 29-10-2018, 13:58   #1
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Join Date: Sep 2017
Location: MD DC area/Annapolis/Baltimore
Boat: 1985 Catalina 27
Posts: 284
Adding ventilation to a holding tank

Has anybody added natural outside ventilation to a holding tank something like the compulsory ventilation of the engine compartment? The little vent in the anchor locker is ridiculously small.
Two 2 1-2" hoses plugged on the top and at each end of the tank and venting outside like the big engine compartment vent hoses would kill the nasty bacteria which thrive in a oxygen deprived environment.
It smells better already!
Your thoughts.
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Old 29-10-2018, 16:26   #2
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Join Date: Feb 2011
Posts: 2,153
Re: Adding ventilation to a holding tank

USCG reqs require that all waste tanks be vented to the outside of the boat. So if yours vents into the anchor locker, it's vented illegally.

The "standard" vent line size is 5/8", but that's only because it's always been the "standard" size vent for water and fuel tanks so the industry just assumed it's also the right size for waste tanks. They're wrong.

You're on the right track with a 1" vent line, but as long as it's short--<5'--straight, doesn't rise more than 45 degrees, and the thru-hull is an open "bulkhead" or "mushroom" thru-hull, one is usually enough. Even better if you can run it forward to a thru-hull about a foot below the toe rail. That would keep air moving in and out of the tank any time you're underway, or on an anchor or a mooring.

All this is described in detail in my book, btw (see link in my signature, just click on the title) and I'm always glad to help you sort out the best way to do it.
2020 Peggie Hall
Specializing in marine sanitation since '87.
Author "The NEW Get Rid of Boat Odors"
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