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Old 24-01-2016, 19:04   #1
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Head holding tank vent thru-hull

I'm looking for a replacement Head holding tank vent thru-hull as ours is corroded pretty badly and I want to up-size it. I haven't been able to find a 3/4" thru-hull with a screen which is all plastic (or Marelon) as I don't want another corroded thru-hull. Does anyone know where I might find one?

thanks!
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Old 24-01-2016, 19:33   #2
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Re: Head holding tank vent thru-hull

So-called "vent"thru-hulls only come in one size: 5/8". That's because they're ALL designed to be used on fuel tanks in addition to water and waste. So you're not gonna find the same kind you have in a 3/4". You do know that you'd have to replace the vent line with a larger diameter hose to fit a larger diameteri thru-hull? That will also require a new vent fitting on the tank. So if you're gonna do this, do it right and go up to a 1" vent.

The short answer to your question: a marelon vent thru-hull is fine. Forget about a screen...they cause more problems than they solve because they clogo up with dust, pollen and...rust. What you want is an open "bulkhead" thru-hull...one that will let you stick a hose nozzle against it and backflush the line into the tank. They come in all sizes, including 5/8" if you decide to just replace the thru-hull.

Installing a larger vent fitting on the tank is actually fairly easy,...thanks to a lil gizmo called the Uniseal UNISEAL Seal the existing fitting with a threaded plug (available from the plumbing dept at any hardware store) wrapped in teflom tape. Some new 1" hose, a 1" thru-hull....voila--new larger tank vent.
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Old 25-01-2016, 13:04   #3
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Re: Head holding tank vent thru-hull

Peggie,

Thanks for the background - it's what I suspected

I can do pretty much anything right now as the holding tank is out and has the fittings removed and all hoses ended up in the garbage to be replaced.

How much better is a 1" vs 3/4" vent in your opinion?
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Old 25-01-2016, 13:23   #4
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Re: Head holding tank vent thru-hull

This uni-seal thing, is it like a grommet, you stick a piece of PVC pipe into it?

I'm soon going to replace my tank etc. and will go to a BIG vent, one I have is as discussed the same as the fuel tank vent, it has two little holes further restricting it.

Good source for I assume a polyethylene tank, one I have from IP is aluminum and I think I'd rather not go back with Aluminum?
Simple rectangular tank.
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Old 25-01-2016, 16:44   #5
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Re: Head holding tank vent thru-hull

That's a very good description of it. I don't recommend using it as a fitting at the bottom of a tank, but it's great for inlet and vent fittings...and it WILL NOT LEAK as long as the hose doesn't pull to a side, top or bottom. That can cause the pvc pipe to break the seal.

(my vent thru-hull) is the same as the fuel tank vent, it has two little holes further restricting it.

Boat builders use the same fuel vent thru-hulls on ALL vents because it costs 'em less than separate ones for each type of tank. That's ok for water, but NOT for waste because waste needs to be managed...water and fuel do not.

Good source for I assume a polyethylene tank, one I have from IP is aluminum and I think I'd rather not go back with Aluminum?

No...you don't want a metal waste tank...urine typically turns any metal waste tank into a colander in an average of about 10 years.

Ronco Plastics (no relation to the VegoMatic Ronco) Ronco Plastics Marine Catalog is your best source for a rotomolded PE tank...they make TOP quality thick-walled (at least 50% thicker than most off-the-shelf or OEM tanks) tanks for a very reasonable price and have more than 400 shapes and sizes, over 100 of which are non-rectangular. And they install fittings in the quantity, sizes and locations specified by the customer when they make the tank. They sell direct to end users...they're also great to work with...we were Ronco distributors for nearly 10 years.

Btw...if you'd like some help improving your existing tank plumbing and venting, give me a shout...I'll be glad to help.
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