Holding Tank Vent

[peghall]

A screen actually creates more problems than it solves because it does get clogged very easily and also makes it all but impossible to backflush the vent line. If you have one, knock it out!

As for the size...5/8" ID has been the standard size for fuel and water tank vents for decades preceding the need for holding tanks...and because it works for fuel and water, the industry--not knowing squat about sewage management--just assumed that 5/8" was also the right size for waste tanks, especially since it lets builders use the same vent thru-hull (that's actually designed to prevent back flames from GAS/Petrol tanks) on all of 'em. So ya pretty much gotta change out the thru-hull, for an open bulkhead fitting, even if it's the same 5/8", to be able to maintain the vent by back flushing it.

[GordMay]

Originally Posted by capn_billl

My sanitation guy stated that dried bits of TP often clog the vent at the waterline of the tank. The only way to fix this is to put pressurised water back down the vent line. He uses a garden hose connected to what looks like a plunger head stuck up against the thru hull to wash these vent lines.

Originally Posted by peghall

... Vents should be backflushed--which cannot be done if a filter is in the line--every time the boat is washed and/or the tank is pumped out.

Indeed.

[nylajo]

Originally Posted by capn_billl

My sanitation guy stated that dried bits of TP often clog the vent at the waterline of the tank. The only way to fix this is to put pressurised water back down the vent line. He uses a garden hose connected to what looks like a plunger head stuck up against the thru hull to wash these vent lines.

Well I've heard it all now, so where is the pressure created supposed to be relieved while doing this? as the deck suction should be going to the bottom of the tank below the liquid level.

[Sailmonkey]

Originally Posted by nylajo

Well I've heard it all now, so where is the pressure created supposed to be relieved while doing this? as the deck suction should be going to the bottom of the tank below the liquid level.

This isnt' uncommon at all, when I pump out the tank I hold a hose over the vent line for a while so that water is sucked in instead of air.

[peghall]

Very little pressure is created by putting just a couple of gallons of water under pressure down the vent line...and what little IS created is relieved as soon as you remove the device. Ordinarily the plunger head wouldn't actually be used as a plunger, but only to cover the thru-hull so that all the water goes down the vent...although I guess it could be used to pull a plug out of the vent that doesn't want to be washed into the tank by back flushing the line. IMO, it's a bit of overkill for any owner, though...at least, it is if you don't ignore the vent till it does get so firmly plugged up that you have to call a pro with a plunger to unclog it.

[US1Fountain]

You are correct Peggie, the hose is indeed 5/8" ID. Brain fade. As with the Sealand check valve description. Again brain fade. I replaced the vent hose and thru hull last winter with new, the thru hull does indeed have screens. In fact, the outter part of the fitting has 2 smaller holes that are only approx 1/4" dia. each. Between those 2 small holes and the screen, this is no doubt the majority of the venting restriction. Thinking possibly this vent is more designed for fuel tank venting, than holding tank?


Thanks for all the replies. Shows me some flaws that will need to be changed.

[peghall]

If you check the marine catalogs you'll see that ALL "vent" thru-hulls are designed for use on fuel tanks...the industry just uses the same thru-hull for all tanks 'cuz it's cheaper and doesn't require the guy who's installing 'em to think about which one should go on which tank.

Btw...if your vent line isn't straight, that should be fixed too. Ideally it should be no longer than 3' (anything up to 5' will be ok, but not great)...straight as an arrow, and no sags in which water or waste can pool. It shouldn't rise more than 45 degrees either...but while that's not too difficult on a powerboat, it can be impossible on a lot of sailboats.

[Therapy]

What diameter vent line would be proper for an 18 gal holding tank?

[davefromoregon]

Originally Posted by Mark Johnson

This is a good point! My wife flushed the head into a 100% full tank once, and it goes right up the vent hoses and down the hull! I used a homemade fitting & garden hose to blast a strong stream of water in the maze fittings, (from the outside), and down the vent hoses. This clears the clog nicely.

Mark

Is there a way to monitor the status of the tank? ie to know how full it is?

[US1Fountain]

Originally Posted by peghall

Btw...if your vent line isn't straight, that should be fixed too. Ideally it should be no longer than 3' (anything up to 5' will be ok, but not great)...straight as an arrow, and no sags in which water or waste can pool. It shouldn't rise more than 45 degrees either...but while that's not too difficult on a powerboat, it can be impossible on a lot of sailboats.

My thru hull is approx 1-1 1/2' directly above the tank, which is located along the hull side, so to eliminate the filter, the vent hose will go straight up and curve at the thru hull. This would prevent the less than 45 degree angle recommendation.

[US1Fountain]

Originally Posted by davefromoregon

Is there a way to monitor the status of the tank? ie to know how full it is?

Both my holding and fresh water tanks have the Tank Watch level indicators. They are indicator lights that indicate empty, 1/2, and full.

[Coachbolt61]

So Peg, where can we go to get up to date information from you?
Smiles
Coachbolt.

[Coachbolt61]

Originally Posted by US1Fountain

Both my holding and fresh water tanks have the Tank Watch level indicators. They are indicator lights that indicate empty, 1/2, and full.

I would have thought better levels would have been empty, 3/4 (look for a pump out) and 7/8 (too late! Get a bucket).
Smiles
Coachbolt.

[peghall]

Originally Posted by davefromoregon

Is there a way to monitor the status of the tank? ie to know how full it is?

There definitely is! Practical Sailor rated the Scad Monitors a couple of years ago: Tank Monitors | Technologies LLC I love these gauges. The beauty of 'em is that the senders are on the outside of the tank, so they can never become clogged by the animal fats in waste as float switch senders do. And, they're affordable. You can get a single tank monitor or one that can handle up to 8 tanks--waste, water and fuel.

Btw, CG regs require that all tanks have a means of determining when they're at least 3/4 full. If access to the tank provides visual inspection, no gauge is needed...otherwise, your'e supposed to have one. However, that's buried so deep in the regs that many CG inspectors don't even know about it.

[peghall]

Originally Posted by davefromoregon

Is there a way to monitor the status of the tank? ie to know how full it is?

There definitely is! Practical Sailor rated the Scad Monitors a couple of years ago: Tank Monitors | Technologies LLC I love these gauges. The beauty of 'em is that the senders are on the outside of the tank, so they can never become clogged by the animal fats in waste as float switch senders do. And, they're affordable. You can get a single tank monitor or one that can handle up to 8 tanks--waste, water and fuel. You can read all about 'em at the link I've provided.

Btw, CG regs require that all tanks have a means of determining when they're at least 3/4 full. If access to the tank provides visual inspection, no gauge is needed...otherwise, your'e supposed to have one. However, that's buried so deep in the regs that many CG inspectors don't even know about it.