Combatting Onboard Toilet Odors

Posted by Darrell Nicholson at 04:01PM - Comments: (13)

Heat brings the stink, so summer is the busy season for Practical Sailor odor-guru Drew Frye.

We’ve had a lot of fun with toilets and sanitation systems in the last couple of years, and after last weekend, when I descended into the smelliest brokerage boat I’d ever set foot on, I thought I’d revisit some of our findings here. The good news is that a stinky head is curable. The better news is that it need not cost you an arm and a leg. That’s not to say a cure is cheap—this is a cruising boat we’re talking about—but in many cases, a change in maintenance habits and less than $20 can put you on the path to deep breathing again.

What follows is just a brief capsule of our recent findings. For more extensive reading, I recommend checking out the full versions of the articles cited below, or one (or both) of the following sources: Peggie Hall’s “Get Rid of Boat Odors” or Volume II of our two-part eBook on marine sanitation.

Odor control doesn’t necessarily start at the marine head (hoses are often the chief culprit), but that seems like the logical place to start. A big step toward reducing head odors is to use fresh water for flushing. Salt water is alive with microscopic critters that add to the odor problem when they die and decay in your holding tank. That is not practical for most long-term cruising boats, but the owner of a big boat with extra tankage can get by with a freshwater flush, particularly if he uses a vacuum-flush toilet system like those we tested in 2011.

The newer electric toilets we tested also cut down on water usage, and just as importantly, they help clear the hose better with their high-velocity flushes. These heads use a high-speed centrifugal “Vortex” pump, which has a unique convex rotor and a funnel-shaped casing or volute that converts kinetic energy into pressure. Akin to a common bilge pump, the centrifugal pump has a set of curved blades on a rotor. The fast-spinning rotor creates a change in pressure that can quickly push a slug of liquid through the system, using very little water and making far less noise than the earlier renditions.

Whether you use fresh or salt water, you will still want to control the chemistry in your holding tank. At the end of last year, we tested several holding tank additives that are effective at controlling odor. Among the products we tested were a few that seemed to help control odors right at the head, and these products would also be effective for portable toilets.

However, you have to be wary about what you add. Our recent test of joker valves—the essential valve that prevents backflow from the holding tank and helps create the vacuum for flushing—demonstrated that some products used for cleaning, deodorizing, and winterizing heads can shorten the valve's life. If you’re serious about controlling head odors, you will watch what you put in your head and replace this valve every year. It is the most important valve in the system.

But to get to the bottom of most head odor problems on older boats, you need to look at the plumbing. Head odors can easily seep through cheap hoses. We conducted a series of tests on two vital hoses—the marine sanitation hose between the head and the holding tank, and the vent hose between the holding tank and the through-hull vent fitting. One of my previous blog posts describes some tips for eliminating hose odors. And finally, we tested holding tanks and holding tank sensors, those trouble-prone devices that tell us when it’s time for a pumpout.

Too often, sailors accept head odors as an inevitable side-effect of having a holding tank. But with a little extra effort you can escape the stink.

Comments (11)

George B., as an Air Head composting toilet user for 7 years, maybe I can answer some of your questions. We are two people using the Air Head full-time. We empty the liquids container every few days, depending on where we are anchored. (If my husband can "go" overboard, he does, which saves us several days on the container.) Many people who anchor out for long lengths of time buy an extra urine container which doubles the timed between having to get to a facility (or offshore) to empty the liquids container. The solids container we empty every 4 to 6 weeks. It is a simple process of turning the container upside down into lawn bags. Depending on where we are, we either empty these bags overboard (offshore, where it is legal) or we dispose of them in dumpsters with other trash. As for the smell that someone commented on, if the liquids container is rinsed well with salt water after every emptying, we have found that a bit of sugar or vinegar (they both work well) helps eliminate the odor. BTW, if you can smell the liquids when it is in place, the unit is not installed correctly. The smell is only for the few minutes that it is not attached to the rest of the toilet. Hope this helps.

Posted by: Connie M. | October 26, 2017 2:35 PM    Report this comment

My experience has been no odor with: two big vents per holding tank, fresh water flush, and quality hoses.

Posted by: David Smyth | October 19, 2017 8:18 PM    Report this comment

Two 1 inch vents, one on each side of the boat, solved my odor problem. The pressure differential from any breeze keeps fresh air in the tank discouraging anaerobic bacteria (the smelly ones).

Posted by: SkipperC | October 12, 2017 10:27 AM    Report this comment

We bought a boat that had two composting heads, and after a few months, had enough of the stink from the urine containers, and the less than pleasant process of emptying the "poop tank". After "digesting" Peggy Hall's excellent book and various other posts, including the "KISS" system, we have now installed two new Raritan "Fresh Head" models, along with new saniflex hoses, and two 1" vent pipes on each tank. The tanks drain by gravity to the Y-valve which either goes overboard, when appropriate, or up to the deck fitting for pump out. This configuration has been so easy, with a minimum of pipes to fight with, thanks to no macerators, and no need for a salt water intake and anti-siphon loop. After 6 months of use, we have had no problems, other than one head that suffered from some back flow. This was due to an imperfect joker valve, which has now been replaced, and all is well in our "headland".

Posted by: Fred T | October 12, 2017 9:55 AM    Report this comment

When you do the composting head, please address how people deal with the urine? Most, by their own admission, just dump it overboard. To meet the same level of a holding tank, composters will need a holding tank for their urine. How many pump-out or proper disposal stations are there for the composting heads? There are countless stories of composters improperly dumping their heads both onshore and in the water. It's like putting a "green" spin removes responsibility.

Following the same rules as holding tanks, the composting head isn't all that attractive. Breaking the rules, sure, but that's just like "bucket and chuckit".

Posted by: James S | September 8, 2013 3:31 PM    Report this comment

I am considering replacing my head and broken Lectra-San with a composting head. I wish PS would do a report on the merits of the competing heads, and more important, a report on how they really work in practice (not just what the brochures say) and the practical value/problems with them (for example, the liquid capacity and how often one might have to empty it somewhere?) My yard is pushing me to strongly consider one as the best alternative to all the odor and repair costs associated with the conventional head. Any other thoughts??? George B

Posted by: George B | August 19, 2013 9:16 PM    Report this comment

This year I had an odor problem I couldn't figure out. I used additives, didn't help. Fresh water flushing, didn't help. Then I found the vent line was clogged so I replaced the old 1/4 " hose with 5/8" hose and bushed up the 1/4" to 5/8" with a short length of black rubber pipe inside the 5/8" sanitary hose in order to make a tight fit. Double clamped it , still had odor. Glued the whole mess shut tight with silicon, still, odor. Then I dis-assembled it all, put in the correct barb (5/8") at the tank, clamped the sanitary hose tight. Voila!. Success. Apparently the little part of rubber hose exposed at the end, albeit inside the sanitary hose, was enough to let odors permeate. It was a small battle won, but it felt like the war was over.

Capt Bob
s/v Zephyr

Posted by: robert b | August 7, 2013 8:02 PM    Report this comment

I just resolved a nasty odor issue when I found that my vent fitting, after 30 years, was totally kaput. The first sign was that I could not manually pump the tank when offshore. When I checked the tank itself, there was positive pressure built up inside.
When I released that, well use your imagination for the odor.
Ed White
Cal 35

Posted by: Ed White | August 7, 2013 3:03 PM    Report this comment

I too hate to think about the $$ invested in maintaining a low odor head. I'm considering a bucket next to the head for $20 contributions per use! One cheap fix is to replace hoses with regular schedule 40 pvc plumbing from the hardware store. I have done this and odor is minimal. I use properly fitted short flexible sanitary hose connections to pumps, thru hulls etc. PVC should not be plumbed so that a failure could flood the boat with seawater. Fasten all pvc well and put a union at a convenient clean out site well above tank level and the water line. My system has been in continuous service for 16 years.
Ken R. August 7,2013

Posted by: KENELM R | August 7, 2013 12:39 PM    Report this comment

Try one cup of Calgon water softening liquid, one cup of HD (non sudsing) liquid detergent and one cup of water. Mix these in translucent water bottle and flush. The HD detergent controls bacteria. The Calgon is keeps the contents of the tank from adhering to the sides. Always pump the tank when it is completely full and flush with at least one tank of clean water. We have been using this method for several years and it works great.

Posted by: Bruce S | August 7, 2013 11:29 AM    Report this comment

A composting toilet will eliminate all those odors as well as the tank itself.

Posted by: MARY H | August 7, 2013 11:02 AM    Report this comment

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