Combatting Onboard Toilet Odors


We’ve had a lot of fun with toilets and boat sanitation systems, most recently with an extensive new reports on desiccating heads and combatting urine odor. And after my experience last weekend while hunting down odors on our new project boat the 1971 S&S designed Yankee 30 Opal, 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. 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: the 2nd Edition of 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.

The newer electric toilets that 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 earlier renditions.  

Whether you use fresh or salt water, you will still want to control the chemistry in your holding tank. We’ve 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 discharge 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 its time for a pumpout.

As it turned out, the problem aboard Opal was not due to any specific component but was caused by a design flaw. Opal initial came with an onboard treatment system and no holding tank, so the holding tank and associated plumbing was retrofitted by a previous owner. The owner located the holding tank vent in the most convenient place, high above the waterline on the hull side nearest the tank. The vent location was also upwind of the forward hatch, so that any associate odors not only wafted over the boat at anchor, but also funneled into the v-berth hatch. There was no vent filter. I plan to install a filter and move the vent further aft, although I’ve also begun looking at composting toilets—which are, as technical editor Drew Frye, points out actually properly called desiccating heads.

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.

Darrell Nicholson
Practical Sailor has been independently testing and reporting on sailboats and sailing gear for more than 50 years. Supported entirely by subscribers, Practical Sailor accepts no advertising. Its independent tests are carried out by experienced sailors and marine industry professionals dedicated to providing objective evaluation and reporting about boats, gear, and the skills required to cross oceans. Practical Sailor is edited by Darrell Nicholson, a long-time liveaboard sailor and trans-Pacific cruiser who has been director of Belvoir Media Group's marine division since 2005. He holds a U.S. Coast Guard 100-ton Master license, has logged tens of thousands of miles in three oceans, and has skippered everything from pilot boats to day charter cats. His weekly blog Inside Practical Sailor offers an inside look at current research and gear tests at Practical Sailor, while his award-winning column,"Rhumb Lines," tracks boating trends and reflects upon the sailing life. He sails a Sparkman & Stephens-designed Yankee 30 out of St. Petersburg, Florida. You can reach him at


  1. Hi, very interesting issue. To have the air vent opening as aft as possible in my boat I use a 25 mm internal diameter , about 4 meters long hose. I changed all hoses with Special Vetus waste hoses, with exception of air vent hose. This is a normal wire reinforced pvc hose, not declared good for thrinking water. Do you mean that this last one could be a crucial point for stinks in the boat?

    • The vent line needs to be the same kind of waste line as any other black water hose. Almost anything else will let the chemical potency of the waste tank seep through, particularly vinyl, but not right away. Vinyl will last a year or two, if you are lucky, but it won’t take long before there are odors and an oddly sticky hose.

  2. I installed the Big Orange vent filter a couple of years ago and it made a lot of difference – cleans up trank vent odor very effectively. One caution though – dont neglect to replace the charcoal filter material annually. It’s hygroscopic and will loose effectiveness if you let it get waterlogged by not changing it out. Also, you dont have to spend $$ for Big Orange charcoal replacement as generic is available on line.

    • The more air the better. Support aerobic bacteria.The gas they produce when breaking down waste doesn’t smell. You notice the vent when anaerobic bacteria has taken over. Usually a result of chemical head treatments and not enough air. I’m also against the vent filter, as it blocks airflow and creates the need for itself

  3. Our boat was built in Europe before holding tanks were typically installed. We found it unconscionable to use the toilet in no-discharge zones so we installed a composting toilet. Zero odors. Not difficult to empty. Low voltage draw. No through-hulls.