Waste Tank Vent Pipe Size ?

[albergsailor]

the origional copper pipe vent was 3/8. Unfortunatly home depot doesnt sell that small of pipe. Im sure i can get it at a plumber supply store. I was almost wondering if 1/2 inch pipe would be better? Just looking for some advice looking to get this fixed soon doesnt smell good after using the head lol. boat is an alberg 30. the waste tank is fiberglass. thanks

[Conall]

1 1/2" would be best. If you are able to let some air in to the tank with a larger vent, you can help the tank stay in an aerobic state which will make things smell better. More oxygen helps the stink eating bugs do more work.

Cheers,

Conall
conallsboatbuild.blogspot.com

[minaret]

1/2" probably would be better, less likely to get clogged. My system uses clear 3/4" hose for the vent, which I like because you can see at a glance that the vent hose is not clogged.

[Cheechako]

1/2 to 5/8 standard venting should be fine. Less opening the better for when the tank gets full and you discover it spewing on deck! What a way to start the morning....

[osirissail]

If you are going to use copper pipe be sure to get the "soft" version and not the hard/rigid stuff. Most boat use vents of vinyl hose to avoid flexing fatigue and difficulty routing the vent from the tank to the overboard vent.

[Cormorant]

Originally Posted by Cheechako

... Less opening the better for when the tank gets full and you discover it spewing on deck!

Do most boats vent their tanks to the deck? Just curious. I installed ours out through the topsides, well aft and well above the waterline.

[osirissail]

Classically vents were installed in the top of the outside of the hull and not on-deck or through the cabin-top. This was generally because it is much easier to route the vent hose thusly. However, many cruisers have found that hull mounted vents are subject to sea water getting back into the tank as the waves wash up and over the hull or in the case of sailboats you put the "rail in the water."
- - The solution was to move the vent to the cabin top or if that is not feasible use a vent fitting that contains an automatic shut off should sea water try to get inside. See: http://www.westmarine.com/webapp/wcs...splayErrorView

[AnchorageGuy]

The larger the vent the less likely you will have smelly issues with the TANK. A minimum of 1 inch ID is recommended and larger if possible. The difference is in how much air gets circulated in the tank. This is the key to controlling the odor so don't skimp on size no matter what it was when the boat was built. These vents were sized for water and fuel tanks in older boats and consideration for holdings tanks were a non issue. A larger vent line will also help to eliminate suction problems in emptying the tank. Be sure and keep it short and no sharp bends. Chuck

[S/V Alchemy]

I am rerouting all tank vents to my pilothouse roof from the "usual" spot under the rail on the hull for exactly this reason, and my plans include a sort of drip loop and petcock just before the final vertical run, plus of course a gooseneck on top. All this will go inside brass poles doubling as handholds inside the pilothouse.

In a similar vein, I am going to have a shut off on my starboard side waterline exhaust so there is no chance of water ingress back up the exhaust circuit if we are sailing well heeled. The shut off lever will engage a circuit on the engine key, so if the exhaust is not open, the engine won't start.

I could rig a solenoid for this, but I prefer all manual. It's also a sort of anti-theft device as few thieves would think (and would find problematic to access if they didn't know about it) a long rod that leads to a yoke that opens and closes a seacock behind a tank.

While this is interesting (ATTWOOD Vent at West Marine), I find, having done a few kerosene flushes due to failed spring and piston combos in anti-siphon loops, that I am happier with straight hoses and high-placed goosenecks if the object is simply to bring outside air pressure to the inside of a tank and to allow a way for condensation to leave.

On a lot of modern sailboats, this is going to be aesthetically displeasing (although one could run the vents into the lazarette out of sight and water), which is why I chose a steel pilothouse, where such considerations aren't really an issue as the thing already looks 3/4 trawler.

[daddle]

Originally Posted by Waterwayguy

The larger the vent the less likely you will have smelly issues with the TANK.

Exactly. While a small vent will satisfy the pressure and pumping issues, a large, short, direct vent will allow a good exchange of fresh air. This will eliminate almost all of the bad smell issues. This is why homes with septic tanks and vents all over the roof generally don't smell at all. How one accomplishes this on the typical small boat is always a problem.