Toilet tank Vent outlet

[tronic72]

Hi,

Im plumbing a tank and I've got most items sorted (vented loops, valves, diverter etc) but am unsure of what to use for the vent outlet. I'm using TruDesign composite fittings for most of the system. The tank vent outlet is 25mm (1 inch) I know some say it should be 1.5 inches but I'm stuck with 25 mm.

Should I just use a through hull fitting with tail like this?

Also, do i locate the outlet as high as possible just below the Gunnel (gunwale)

[wingless]

The three important considerations for the tank vent are: a constant uphill slope from the tank w/ no valleys; provide for low-volume charcoal filtered air exhaust when fluid added and provide high-volume air inlet during pump out.

The potential issue when using smaller than recommended hose diameter is when the tank is being pumped out by the extra-high-speed dock pumpout stations. If the vent air is too restrictive, then it is possible to collapse the tank. My Vacuflush tank has a vent relief valve on the top surface to protect the tank under severe pumpout conditions.

The factory-installed vent hose on my Vacuflush system is small, about 1/2" ID and it has been fine. I have never heard the relief valve open.

[Cheechako]

Below the gunnel would end up with some intake of water when heeled I would think?

[tronic72]

Originally Posted by Cheechako

Below the gunnel would end up with some intake of water when heeled I would think?

Not high enough? Boat is a 32 foot fly bridge cruiser. Should it be above the gunnels close to the window base? Was the through hull the correct outlet?

[Cheechako]

Originally Posted by tronic72

Not high enough? Boat is a 32 foot fly bridge cruiser. Should it be above the gunnels close to the window base? Was the through hull the correct outlet?

Should be fine, I thought it was a saillboat.

[wingless]

This fitting is similar to the one the factory installed on my boat.

It is important that the vent prevents water intrusion. Once the charcoal filter gets wet, then the filter must be tossed.

[peghall]

Should I just use a through hull fitting with tail like this?

Yes...and 1" is an adequate size for the vent. It allows the free exchange of air necessary to keep the the tank aerobic and also has one more benefit: prevents vent line blockages by allowing you to put a hose nozzle against it and backflush the vent line every time you pump out and/or wash the boat.

Also, do i locate the outlet as high as possible just below the Gunnel (gunwale)?

Since your boat doesn't heel, the vent line should be as short, straight and as close to horizontal as possible...so put the thru-hull only as high as it needs to be to prevent water intrusion when you're underway.

Where will the tank be located in the boat? How far (hose length) from the toilet? If you'd like to discuss in more detail than is practical in a forum discussion, you're welcome to contact me directly.

Peggie
"If you can't explain it to a six year old, you don't completely understand it yourself." --Albert Einstein
http://www.amazon.com/New-Get-Rid-Bo...dp/1892399784/

[S/V Alchemy]

Originally Posted by Cheechako

Below the gunnel would end up with some intake of water when heeled I would think?

This is why you want a gooseneck for that vent line.

[YellowcakeMan]

Like wingless said, be sure the hose rises from the tank with no dips or valleys. If not, you will get sewage in the line which won't drain back to the tank, and when you add to the tank, that sewage will spray out of the vent. This mistake was made with one of our tanks during a professional refit. We had to go back and re-route the line ... and clean lots of sewage spray off the hull.

[JOHNMARDALL]

Lots of good advice here. To prevent holding tank fumes getting into the cockpit and nauseating the occupants, mount the vent outlet on or near the transom, or install a "no-smell" activated carbon filter in the vent line, or both.

Good luck
John Mardall
Vetus Maxwell Group

[peghall]

Originally Posted by S/V Alchemy

This is why you want a gooseneck for that vent line.

A gooseneck is recommended in fuel and water tank vent lines, but not in a waste tank vent because it would prevent the exchange of air needed to maintain the aerobic environment needed to prevent odor from occurring. On a sailboat, the vent thru-hull needs to be high enough on the hull to keep it out of the water a max heel...if you heel enough to put your rails in the water a high clamshell does the job. No need to worry about splashing onto the vent thru-hull. You wouldn't want even the tiny amount of water that could put into a fuel or water tank, but it doesn't matter if it gets into the waste tank.

...be sure the hose rises from the tank with no dips or valleys. If not, you will get sewage in the line which won't drain back to the tank, and when you add to the tank, that sewage will spray out of the vent.

Nothing can spill into the vent line if the vent fitting on the tank is at the edge closest to the CENTERLINE of the boat...'cuz when the boat heels to one side, tank contents run away from the vent fitting...when heeled to the other side, the vent line runs uphill. Also putting the inlet fitting from the toilet at an edge closest to the centerline will also prevent contents from running back toward the toilet when heeled.

To prevent holding tank fumes getting into the cockpit and nauseating the occupants, mount the vent outlet on or near the transom, or install a "no-smell" activated carbon filter in the vent line, or both.

Doing either would actually create odor...you'd only be blocking or redirecting it. What you really want to do is prevent odor from occurring in the first place...and the key to that is oxygen. When organic matter breaks down aerobically (oxygenated), it converts to CO2 which is odorless. It can only generate noxious--and also toxic--gasses in anaerobic (airless) conditions. So a short straight 1" vent line that allows plenty of air exchange with the gasses in the tank will create the aerobic environment necessary to insure that those gasses are odorless.

Peggie
"If you can't explain it to a six year old, you don't completely understand it yourself." --Albert Einstein
http://www.amazon.com/New-Get-Rid-Bo...dp/1892399784/

[Davidhoy]

I learn something new every time I read one of Peg's responses

[tronic72]

Thanks everyone for the replies.

The tank sits about 2 feet below and slightly towards the rear of the head on the starboard side. The head is located about a third of the way from the bow.

Given the importance of the line not kinking, would I be better off using a normal threaded through hull with a right angle like the one attached??



This would mean the venting hose could go directly straight up from the tank without any bends at all.

Thanks again.

[wingless]

Originally Posted by wingless

This fitting is similar to the one the factory installed on my boat.

It is important that the vent prevents water intrusion. Once the charcoal filter gets wet, then the filter must be tossed.

Originally Posted by tronic72

Given the importance of the line not kinking, would I be better off using a normal threaded through hull with a right angle like the one attached??

This would mean the venting hose could go directly straight up from the tank without any bends at all.

Or, use a fitting like I've linked, with the bend as part of the fitting.

The one on my boat is similar, except it has a downward-facing cup w/ a screen.

[tronic72]

Originally Posted by wingless

Or, use a fitting like I've linked, with the bend as part of the fitting.



The one on my boat is similar, except it has a downward-facing cup w/ a screen.

Hi Wing sorry I missed your original link. The one in your link won't work as the outlet is 1" (25mm). But that looks almost the same as what I'm proposing but without a shroud covering the outlet. Thanks.