I am ordering a replacement holding tank today, and am wondering again why the vents on the tanks come 1/2" or 3/4", and the through hull vents all come sized for 5/8" hose?
Holding tank vents?
- Thread starter Scott21120
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I think you'll find the 1/2" tank fittings will
fit 5/8" hose...that the threaded end is 1/2" OD, but the barbed end is 1/2" ID...making the OD 5/8". However, I'd specify at least a 1" vent on your new tank. That will mean you'll need to use an open bulkhead fitting instead of a "vent" fitting, but that's ok. Why are all "vent" thru-hulls 5/8"? Because eons ago--long before there were holding tanks--someone decided to make that the standard size for water and fuel tank vents. So when holding tanks came along, they just made the vents on 'em the same size as fuel and water. All vent thru-hulls are actually designed for use on fuel tank vents, but because they can also be used for water and waste tank vents, boat builders can buy the same one in quantity, which costs 'em less than buying different thru-hulls for each type of tank. That waste tanks need more air than than a 5/8" vent OR that type of thru-hull can provide makes no difference...they're gonna go with what costs 'em less. It's only been in the last few years, as the industry began to learn that waste, unlike fuel and water, must be managed to prevent odor, that you could find a TANK that has even a 3/4" vent...1" or larger, or two vents, are only available on special order tanks. And you still have to use a bulkhead thru-hull instead of a "vent" thru-hull for any vent line larger than 5/8". Before you order the tank you might want to check out the link below.
fit 5/8" hose...that the threaded end is 1/2" OD, but the barbed end is 1/2" ID...making the OD 5/8". However, I'd specify at least a 1" vent on your new tank. That will mean you'll need to use an open bulkhead fitting instead of a "vent" fitting, but that's ok. Why are all "vent" thru-hulls 5/8"? Because eons ago--long before there were holding tanks--someone decided to make that the standard size for water and fuel tank vents. So when holding tanks came along, they just made the vents on 'em the same size as fuel and water. All vent thru-hulls are actually designed for use on fuel tank vents, but because they can also be used for water and waste tank vents, boat builders can buy the same one in quantity, which costs 'em less than buying different thru-hulls for each type of tank. That waste tanks need more air than than a 5/8" vent OR that type of thru-hull can provide makes no difference...they're gonna go with what costs 'em less. It's only been in the last few years, as the industry began to learn that waste, unlike fuel and water, must be managed to prevent odor, that you could find a TANK that has even a 3/4" vent...1" or larger, or two vents, are only available on special order tanks. And you still have to use a bulkhead thru-hull instead of a "vent" thru-hull for any vent line larger than 5/8". Before you order the tank you might want to check out the link below.
Larger holding tank vent
When I replaced the tank in my boat, I followed Peggie's advice and went with a 1" vent fitting. The fitting, connected to 1" hose, went to a standard thru hull fitting high on the side of the boat, well above the water line even when heeled. (Well, maybe not when REALLY burying the rail!). The largest advantage that I've found, above and beyond increased airflow to the tank, is that when I pump out, I can stick a standard 3/4" hose in that thru hull and rinse/clear the vent while pumping out. Actually, once I get the tank empty, I stick the hose in the vent and continue pumping for another minute of two until all that is coming through the pumpout is clear water, and I know that there is nothing left in the tank. BTW, I think I used LifeCaulk to put that thru hull on and not 4200/5200, but that's for another thread. T J
When I replaced the tank in my boat, I followed Peggie's advice and went with a 1" vent fitting. The fitting, connected to 1" hose, went to a standard thru hull fitting high on the side of the boat, well above the water line even when heeled. (Well, maybe not when REALLY burying the rail!). The largest advantage that I've found, above and beyond increased airflow to the tank, is that when I pump out, I can stick a standard 3/4" hose in that thru hull and rinse/clear the vent while pumping out. Actually, once I get the tank empty, I stick the hose in the vent and continue pumping for another minute of two until all that is coming through the pumpout is clear water, and I know that there is nothing left in the tank. BTW, I think I used LifeCaulk to put that thru hull on and not 4200/5200, but that's for another thread. T J
After buying Peggie's book last year
I added a second vent to the old tank. Since my vents have to go up at a fairly steep angle, I vented one on the port side and one on starboard, with one vent facing forward and one aft. Since we are on a mooring, I figured the forward facing one should always have air blowing into it, which should exhaust out the rear facing vent. If I spec the new tank with 2) 1" vents, and use conventional through hulls, I will lose that small advantage, will it be offset by the larger diameter?
I added a second vent to the old tank. Since my vents have to go up at a fairly steep angle, I vented one on the port side and one on starboard, with one vent facing forward and one aft. Since we are on a mooring, I figured the forward facing one should always have air blowing into it, which should exhaust out the rear facing vent. If I spec the new tank with 2) 1" vents, and use conventional through hulls, I will lose that small advantage, will it be offset by the larger diameter?
What do you mean by "conventional thruhulls?"
If you mean "vent" thruhulls, you lose all the advantage of a larger diameter vent line. The good news when it comes to replacing a smaller vent thru-hull with a larger one is, it's a LOT easier to make a smaller hole in the boat larger than it is to make a larger hole smaller.
If you mean "vent" thruhulls, you lose all the advantage of a larger diameter vent line. The good news when it comes to replacing a smaller vent thru-hull with a larger one is, it's a LOT easier to make a smaller hole in the boat larger than it is to make a larger hole smaller.
I'm sorry - what I meant was
even though I have the 5/8" vents - one is always facing into the wind so I have a "forced air" advantage. Would that be offset by replacing the 5/8" vents with straight through hulls of a larger diameter? It seems like the straight through hulls will be even more passive - since neither one will be directly oriented into the wind while on the mooring. Does that make sense?
even though I have the 5/8" vents - one is always facing into the wind so I have a "forced air" advantage. Would that be offset by replacing the 5/8" vents with straight through hulls of a larger diameter? It seems like the straight through hulls will be even more passive - since neither one will be directly oriented into the wind while on the mooring. Does that make sense?
It depends on several factors...
Starting with the design of the thru-hull. If it's one that only has a slit in the bottom or aft side, no air will get in no matter which way the boat is aimed....that slit can't face forward, or water will be forced into the vent line if the thru-hull is buried when you're heeled. How long the vent line, and how straight, are two more factors. It makes no sense that you'd have a "forced air advantage" while underway, but not on a mooring...'cuz on moorings or at anchor, boats are always headed into the wind....in which case, an open thru-hull will do the best job of keeping the tank aerobic. Where do you plan to put the tank? Where does the vent exit the hull? Wanna move this to email to discuss your proposed installation in more detail than is practical in a discussion forum? I'm in all the owners directories, you can email me from there.
Starting with the design of the thru-hull. If it's one that only has a slit in the bottom or aft side, no air will get in no matter which way the boat is aimed....that slit can't face forward, or water will be forced into the vent line if the thru-hull is buried when you're heeled. How long the vent line, and how straight, are two more factors. It makes no sense that you'd have a "forced air advantage" while underway, but not on a mooring...'cuz on moorings or at anchor, boats are always headed into the wind....in which case, an open thru-hull will do the best job of keeping the tank aerobic. Where do you plan to put the tank? Where does the vent exit the hull? Wanna move this to email to discuss your proposed installation in more detail than is practical in a discussion forum? I'm in all the owners directories, you can email me from there.
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