I seem to get frequent blockages in my holding tank vent despite running a hose into the fitting when I can. I suspect poor design but the area is very hard to reach, so I have been dreaming up alternatives that don't require contortions. Is there any point in modifying a deck cap for the pumpout with a second vent, or would the value be instantly negated when the bottom of the pipe is under fluids?
Waste Cap vent?
- Thread starter danm1
- Start date
Assuming your tank is correctly plumbed (Vent and inlet from the head near the top of the tank and outlet at or near the bottom.), I think you’ve identified the primary flaw in your idea of adding a second vent at the waste deck cap.
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Is the vent thru-hull the standard 5/8" that's the same as the ones on your water and fuel tank vents? Those are actually designed to keep sea water out of your fuel and water tanks, making them a bad choice for use on holding tank vents for two reasons 1. they're one of the two most common location for a vent blockage, but boat builders use the same vent thru-hull on all vents 'cuz it saves a little money...and 2. they prevent the free exchange of air with the gasses in the tank that's essential for preventing odor. The solution: replace it with an open bulkhead (aka "mushroom") fitting. This not only improves the ventilation, but also allows you to prevent vent blockages by putting a hose nozzle against it regularly to back flush the vent line...sending anything that's trying to set up housekeeping in it into the tank.
The other common location for a vent blockage, especially on sailboats, is the other end of the vent line--that end of the hose and the vent fitting on the tank 'cuz heeling and/or over-filling the tank allows tank contents to flow into it. That one is a bit harder to clean out 'cuz it requires removing the vent line from the tank and scraping the hose and fitting out manually. The good news is, back flushing the vent line often makes that unnecessary.
--Peggie
I like the idea of being able to back flush the waste tank vent line, but the standard clam shell shielded through hull vent on my boat also has an insect screen. Same at the water tank fuel tank vents actually. Are you saying that the screen is really not necessary or just that the risk of insects is the lesser of two evils when it comes to the waste tank vent?
I couldn't get to the hose to change the deck fitting because the PO installed the davits so I can't open the hatch necessary for access (don't ask) so I hacksawed off the clamshell cover to be able to flush the vent line directly. It definitely was blocked, definitely was cleared, and the odor dissipated. But the opening is still small and I switched to odorlos because it's supposed to be better with low oxygen. Anyway, it worked great when cruising, but I'm still getting a nasty odor from the vent when the boat is sitting. The smells are definitely from the vent and not inside the boat.
I'm actually saying both...and I'm adding that screens are a bad idea on holding tank vent thru-hulls because they get clogged with dust, pollen and--in the event of a spill out the vent--tank contents.
--Peggie
It may be fairly easy to fix that problem... Where is tank located in your boat?
....How long is your vent line? Is it straight or have bends in it? Does it rise more vertically than 45 degrees? How far forward or aft on the hull is the vent thru-hull?
--Peggie
It's a Hunter 356. Tank is in the starboard aft swim platform locker and the vent is above it on the coaming. Hard to tell from what's visible, but I think the vent hose runs fairly straight for just a few feet and at about 45 degree or a little steeper. I can't see where hose meets the vent inside, so I don't know if there is an elbow or straight connection.
Are you open to finding a location for it and running some new plumbing? If so, send me a PM.
--Peggie
--Peggie