Head holding tank vent thru-hull

[geoffr]

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!

[peghall]

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.

[geoffr]

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?

[a64pilot]

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.

[peghall]

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.

[I36guy]

I'm reconfiguring the tank vent(s) on my holding tank. I've decided to go with dual 1" vent hoses. The tank ports (uniseal) are on the outer edges of the top of the V-shaped tank.

Conventional wisdom says to run the hoses as near to horizontal as possible, for as short of length as possible - venting to the side opposite of the vent port in the tank.

On my boat this means the port will be about 12" above the waterline at rest and under water under sail. Since the "horizontal" hose will be inclined under sail, the port associated with the submerged vent hole will ALWAYS be above the water line.

I can run the vent lines to a point near the toe-rail but, if I cross-plumb the vent lines, this increases the hose length by 2X and the run will be vertical in some places.

I can also run the hose from the tank fittings to the near-side hull just below the toe-rail. My worry is that if the rail is the water (which should be rare), water will ingress directly to the tank (or exit the tank if it is full.

Should I:

1. install the vent holes cross-plumbed near the waterline?

2. Run the vent line cross-plumbed to just below the toe-rail?

3. Run the vent to the near side hull just below the toe-rail?

[peghall]

You're on the right track, but not quite how I'd do it. For one thing, you shouldn't need two vents and some of what you've described can create more problems than it solves. You've mentioned a couple of things.

Where's the tank located in located in the boat?

If you'd like to brainstorm in more detail than is practical in a discussion forum, PM or email me.

--Peggie

[Nicholson58]

Two vents with one under sounds like a possibl siphon.

We went single vent high and centered aft. No problems.

[mottseng]

Originally Posted by geoffr

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!

I did exactly what you are suggesting. I too took my tank out and had new very robust fittings plastic welded on replacing the old ones. At the same time I went with a 3/4" vent fitting. After speaking with Peggy I went with a non-screen 3/4" thru hull fitting and replaced all the hoses. I also installed a SCAD tank monitor.

Very happy to report that all is working perfectly and I have complete peace of mind when using the head.

[Nicholson58]

I used a 1/2 inch Groco. They are not expensive.

The shiny ones with a screen are for gasoline. The screen is a flame arrestor. You do not need it. When the screen gets plugged with spider webs you smelly troubles begin

[hattiews]

Originally Posted by peghall

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.

Hi Peggie,
I am working on a similar project connecting a vent hose for the water tank, that was previously coiled in a closet.I'm planning to have the vent located on the vertical edge of the cabin top, right above where the deck fill is located.
Are there any issues with using a plastic fitting? I'm looking for a 5/8" 90 degree fitting and the closest to what I want is a RULE INDUSTRIES barbed Plastic Mushroom Head thru-hull.
I have heard disparaging comments about plastic fittings and I'm curious whether they are well founded or not?
Thanks!

[peghall]

You can use plastic as long it's not nylon....it's ok for tank fittings and other uses inside the hull. , but Nylon fittings aren't UV resistant so sunlight turns 'em into powder. Marelon would be your best choice.



As for where to put the thru-hull and the type of thru-hull. I'd keep the vent line fairly short and--unlike a waste tank vent line--put a high arch in it close to the thru-hull..that's to prevent rain or seawater from getting into the water tank. The thru-hull should also be one that's designed to keep water out. If the Rule thru-hull is an open bulkhead or "mushroom" fitting, it's not the right kind. Look for fuel tank vent thru-hulls...they're designed to keep sea water out of the vent line and also what boat builders use on all tanks. Finding one that's a 90 degree fitting may be challenging though...you may just have to use a 90 degree thread-barb hose fitting on it.


--Peggie

[bluenoser613]

Looking at your thread here, would this fitting be sufficient for a holding tank vent?

https://www.marineoutfitters.ca/inde...e=085226020728

[peghall]

No. Only one thru-hull is actually suitable for a holding tank vent: a bulkhead or "mushroom" thru-hull.

There are two reasons: 1. an open thru-hull allows the air exchange necessary to maintain the aerobic conditions in the tank to prevent odor...and 2. it allows you to put a hose nozzle against to back flush the vent line every time you wash the boat and/or pump out, preventing vent blockages.


--Peggie

[peghall]

How much better is a 1" vs 3/4" vent in your opinion?


The bigger the better...within the limits of how large a hole any of are willing to put in the sides of our boats!


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.

If you have enough clearance above the tank (up to 5" for 1.5" fittings). I'd put all the fittings on the top of the tank...or at least the vent fitting. For one thing, that'll increase the useable capacity of the tank at least another gal vs a vent fitting on a side or end. It's actually fairly easy to relocate tank fittings, thanks to a li'l gizmo called the Uniseal...I'll walk you through it if you want to send me a PM.


--Peggie