Holding tank vent odors

12 years 4 months ago #1193 by Scott Lee
This was a recent discussion on the Whitby 42 Facebook page about holding tank odors and different solutions. It was started by George on Indefatigable and I am sharing it here in hopes of helping anyone else fighting these issues and also to see if anyone else has any other advice.

Joie de Vivre #88

George Chamberlain:
Head smell! My holding tank vent was plugged from many years of over filling the holding tank. When I went to clean it out and figure out the head smell issue, the through hull fitting (a tiny bronze elbow fitting in the transom) broke off. So I re-routed the holding tank vent into the propane locker, and installed a tank monitor. The new location makes it easy to backflush the vent line when we pump out, and because the propane locker is vented overboard, this "should" cure the head smell issue, right? Well, the downside is that there is little, if any, air exchange, so the tank is pretty much anaerobic, so it smells when you flush. And a secondary issue - haven't decided if it's good or bad - is that it stinks in the aft cabin when you flush, so I figure the propane locker is not sealed very well. (I plan to seal that up with epoxy, we don't need a propane leak ending up in the bilge...) My long term "solution" for the head vent is to install a second vent line to bring air in from the new transom through hull, and exhaust it into the propane locker, by also installing a a solar vent in the propane locker lid. The solar vent would be set on "suck" - so it would pull air in from the transom through hull, through the second vent line, through the tank, and out the existing vent line into the propane locker, and then overboard via the solar vent. If I had a propane leak, presumably it would exit the locker the same way - through the solar vent - or else it would sink to the bottom of the locker and run out the existing drain hole.

For all the Whitby owners out there - how is your holding tank vented? Does it work for you, or do you have issues? Does anyone have comments on my "plan" - it may be a bit overengineered, but I think it will work...what do you think?

Gerry ODonoghue:
Hi George, sounds like you are having fun. Just two points; 

1. The size of the vent will make no difference to the anaerobic / aerobic state of the tank. The hose is just too small to cause air circulation. I presume that your tank is under the main ladder in the usual position. I would just route the vent to the cockpit cowling via a charcoal filter. You can buy a standard filter or make your own using pvc pipe.
This will take care of the smell.

2. If you want to use the LPG locker you need to check the hole that the LPG hose goes through. I bet you will find that this is not sealed. This will cause smells in the aft cabin. In any case you need to make sure that this is a sealed hose gland. 

Best regards

March 13 at 10:28pm

George Chamberlain:
Thanks, Gerry. I will check that there is a hose gland - this would be an issue in its own right, and more serious than the head smell. As for the hose size, I think you're right, because of the excessive length to the through hull, whether through the transom or into the locker. I expect that by the air to circulate, the small hose(s) won't be a problem.
March 14 at 6:01am

Ed Watson:
Shortest hose runs for shit hoses are always the best. Mine exits out the side, just under the rubrail. I don't know how much time you spend sailing with your rail in the water, but it has never been a problem for me.
March 14 at 6:38am

Steven Fred Lott:
Hose diameter.... Hmm... We've got a new fuel vent hose. Perhaps we should replace the holding tank vent hose with something larger. That does mean taking the port side of the aft cabin apart again (Argh!)
March 14 at 7:06am

Rick Middleton:
Hey George, another option is to convert to a composting head. We replaced our aft head with a NatureHead about 18 months ago. Initially we unhooked and plugged the discharge and water intake hoses and left them in place in case we weren't satisfied with the results. Simply put, the NatureHead works as advertised and is virtually odor free. We have no intention of going back to a holding tank system. We left the forward head as is, but do not use it. When I get the motivation, I will remove it and the empty tank. The one down side to the NatureHead is size, a bigger footprint and a higher profile. We solved this with a small support in front and a stool to climb upon the throne.
March 14 at 9:27am

Cindy Ann Bowers :
@Rick - thanks for the recommendation on the NatureHead. It's on my wish list.
March 14 at 10:44am

Gerry ODonoghue:
Cindy, Bill and Judy (Janus) have a composting head installed and are well pleased. It was on my wish list but the boss vetoed the ides. My only concern is disposing of partially composted waste in marina dumpsters etc. at some stage someone will get bent out of shape over this issue.
March 14 at 11:23am

Justin Smith:
My vent was plugged because it ran from the tank along the bottom of the boat to the transom. I removed the line ran a new vent line and put it right next to the port cockpit drain. It has been working great. I also used 5/8 hose line.
March 14 at 12:47pm

George Chamberlain:
Justin - does your holding tank vent into the floor of the cockpit locker? Or does your cockpit locker drain to a through hull above the waterline, and the vent goes there too? My cocpit drains are below the waterline. Or does it tee into the drain line?
March 14 at 1:27pm

Justin Smith: 
I'm sorry I ment it is right next to the deck drain port side. I hardly ever get the rail under so I figured it was a good place for it.
March 14 at 1:50pm

Scott Lee:
 We too switched out our aft head with a natures head and love it. No smell and no pump outs! Yeah! We do plan on keeping the front head routed to the holding tank though. With the natures head I need to dump the urine container daily... Er... Nightly. Typically this goes overboard but in busy harbors and marinas I feel a bit guilty about dumping two gallons of pee in the water every day. In these situations, if pump outs are convenient, we will continue to use our forward head and holding tank.
I also routed my holding tank vent line to the side of the cockpit coaming. This is a better location for the line to vent but it has been much worse for the smell as the cockpit is nearly uninhabitable for a couple minutes after flushing. I will be looking into the charcoal filter that Gerry mentioned.
March 14 at 5:05pm

Terry Temperly:

Recall that propane is heavier than air, that's why it would collect in the bilge. In a separate locker, there should be a hole at the bottom of the locker to let the gas go overboard. The locker is not designed to be sealed tightly, and the top may even be open, but not a problem for propane, it goes out the hole near the bottom of the locker. But your head gas will come up over the top of the propane locker.

I'm not so sure it is a good idea to try and pull vapors up with a solar fan. (okay for head gas, but what about propane?)

March 14 at 7:04pm

Gerry ODonoghue:
 Holding tank filter; clubsearay.com/showthread.php/849-How-to...s?highlight=recharge Good to sea that Sea Ray owners are as cheap as us blow boaters. Hi Terry. I agree with you about the propane locker not being totally sealed, but it MUST be sealed from the inside of the boat. All owners should check that the holes that the LPG hose and the solenoid power supply go through are compression glands as they exit the locker and travel inside the boat. I also plan to enlarge the drain hole in the transom as it frequently gets clogged.

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March 14 at 7:29pm

George Chamberlain:
Terry: there is a drain hole at the bottom outboard (port) corner of the propane locker for the gas. The head vent comes in at the top near centerline. I don't know if the solar vent is ignition protected, that's a good point. The reason why it would be set to "suck" of course is so it wouldn't push propane into the holding tank in the event of a leak. I expect that if there was a slow propane leak, it would go to the bottom of the locker and out the drain, probably even with the fan running. But with a more dramatic leak, the fan not being ignition protected could be a bad thing. I'll have to check on the fan specs but I imagine it is not ignition protected.
March 14 at 7:32pm

Gerry ODonoghue:

TRIDENT RUBBER Vapor Tight Straight-Through Fittings at West Marine
March 14 at 7:35pm

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