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Getting rid of boat Odors


Jun 1, 2004
Catalina 27 Mission Bay, San Diego
I scanned this article from our latest marina newsletter( a syndicated publication to which Marina Village subscribes).... Besides the subject matter, which is an important recurring topic here on SBO, I found it refreshing that the author gives OUR Peggie Hall a huge plug for her book and nom de plume.(Step 10) Hopefully, it's not because he lifted too much, verbatim, from her treatise on the subject of boat odors...heh, heh. Oh, and there's a funny typo in the final paragraph... can you spot it?

The Top 10 Steps to Help Rid Your Boat of Odors
- By Michael McNeil
It's one of the most common complaints I hear from boat owners. Especially from the women of the boat.

Eliminating boat odors can be a frustrating exercise, especially if you don't know where they are coming from. Worse, if not fixed fairly quickly, smells can permeate the upholstery and wood inside the boat and remain for long periods of time.

If you can't identify the source the common response is to over compensate, wasting time & money.

First things first. Check all the possible odor sources.
And there are many. The most common sources of course are the head, sanitation hoses, holding tanks and bilges, but smells can also come from a large number of other sources which I will also address here.

Let's start with the sanitation system:
Lots of websites, marine retailers and general retailers will be happy to sell you an amazing array of "stuff" designed to cover up smells, but not necessarily eliminate them. A red flag is any product that says "eliminates odor" but have powerful scents added to them.

Be wary of these unless you prefer your boat smell like an elderly lady reeking of too much perfume to cover odors! Even mechanical devices like ozone generators or air purifiers in the boat may work great, but if you don't eliminate the source of the odor, it will reappear every time you re-open the boat after being away a bit. So here the tips to help rid your boat of odors.

Step 1: Pump out the holding tank and treat the system with 8 or 10 ounces of Odorlos brand or KO Brand chemical treatments.

There are really only two types of holding tank treatments. Chemical poisons that kill every living thing in the tank. Biologic agents are living aerobic bacteria (the kind that don't produce odors as they grow).

These guys eventually kill off the anaerobic bacteria and take over the tank. It takes longer (2-3 weeks) and you can kill them accidentally by using the wrong types of toilet cleaners or treatments.

Seazyme has worked well often where the chemical agents don't always get it done. You can know they are thriving if your holding tank discharge becomes very dark, almost black in color. Almost any treatment that has "zyme" as part of its name is a biological treatment and should not be used with other treatments or toilet cleaners that are not biodegradable.

Like bleach. (more on that later). Give them a day or two (chemicals) to a week or two (biologic) to work. This may not solve your problem but it will make further inspection less offensive.

Step 2: Use Raritan's CP (cleans potties) both to clean the head and also down the sink and shower drains to keep them smelling fresh. If you have a shower sump, be sure to check it and scrub it out. This is an easy place for mold and mildew to accumulate so beware!

Step 3: If neither treatment is working you should try to "back-flush" the holding tank. Start by pumping out the holding tank until empty, then add water from a garden hose back into the tank through pump-out deck fitting for 30-60 seconds at a strong rate of flow.

Pump the tank again and repeat this process until the fluid out becomes clear or as clear as reasonably possible in the time you have to perform the flushing. Some larger tanks can take a dozen or more such cycles to achieve acceptable results. (Tip:) This procedure can also remove years of solids build up from the bottom of the tank.

Step 4: Shock treatment. Wave action can play havoc with boats with waste holding tanks. The contents of the tanks can easily become plastered on the walls and ceilings of these tanks.

Once back in the harbor the head chemical runs to the bottom of the tank and there is literally no odor protection on the other surfaces. These surfaces can become crusted and form ledges where all manner of growth activity happen. There is a very effective, proven, solution, developed originally by Head-O-Matic for the airline industry, that works. One bottle poured into the head will solve this problem.

Every holding tank should be shock treated each fall, prior to haul-out or off season storage or no use to help clean the hoses and all these internal holding tank surfaces. The best time to do it is a week or so prior to your last pump out.

You want the contents of the bottle to
slosh about in the tank, on your last few runs, to ensure all of the tank surfaces are treated. It also helps de-scale and deodorize the inside of the head hoses.

(Tip: On using chlorine bleach.) Many people are concerned about adding bleach to the tank and the waste handling system as a whole. The argument used is that mixing bleach and ammonia is extremely dangerous, since toxic vapors will be produced. The primary toxic chemical formed by the reaction of chlorine and ammonia is chloramine vapor, with a potential for hydrazine formation.

Bleach kills germs and bleaches fabrics and other surfaces. It's wrong to call household bleach chlorine bleach because it has an entirely different chemistry.

Household bleach is derived from sodium chloride – common table salt, not sodium hypochlorite. Normal bleach contains this ingredient in a concentration of 5 to 10 percent, according to the Clorox Co. Clorox purchases chlorine and makes household bleach by bubbling the chlorine into a solution of water and sodium hydroxide.

During this process, all of the chlorine is converted to a sodium hypochlorite solution Household bleach begins and ends as salt water in a fully sustainable cycle. During consumer use and disposal, about 95 percent to 98 percent of household bleach quickly breaks down.

Another assertion is that bleach tends to degrade certain plastics and make them "brittle".

The majority of Clorox® bleach products contain anticorrosion agents and, when used as directed, are safe for use on a variety of hard, nonporous surfaces, including stainless steel, plastics, glazed ceramics, glass, porcelain and other materials.


When mixed with ammonia, drain cleaners or other acids, chlorine (sodium hypochlorite) reacts to form dangerous gases called chloramines, according to the Washington State Department of Health.

Because of the ammonia contained in urine, cleaning urine of any kind, including urine, results in noxious fumes due to the production of chloramine gas.

Mixing bleach and ammonia (present in urine) is extremely dangerous, since toxic vapors will be produced. The primary toxic chemical formed by the reaction is chloramine vapor, with a potential for hydrazine formation. The bleach decomposes to form hydrochloric acid, which reacts with ammonia to form toxic chloramine fumes.

And while urine present in a toilet doesn't contain enough ammonia to be a problem when mixed with chlorine bleach. But ammonia is created when urine is left stagnant taking days or weeks to become laden with ammonia. Like when stored in the holding tank.

If ammonia is present in excess (which it may or may not be, depending on your mixture), toxic and potentially explosive liquid hydrazine may be formed. While impure hydrazine tends not to explode, it's still toxic, plus it can boil and spray hot toxic liquid.

Step 5: Make sure that the vent hose is not blocked. First check that the exterior vent is not blocked. Dirt, corroded fittings or screens, excessive wax or polish even a spider nest can cause this to be inoperable, forcing the odor back into the boat every time you flush. It's also possible that sludge or an accumulation of toilet tissue could block the vent hose or its connecting fitting at the tank.

If the exterior vent is clear, disconnect the hose at the tank fitting and make sure that it's not blocked there. Try blowing air through the hose from the tank to the thru-hull fitting. (Never pressurize the tank with compressed air). If the hose is blocked then replacement is in order.

Make sure that all hoses have no sags or loops, and that the vent hose runs uphill from the tank to the thru-hull fitting. Check for tight hose clamps and don't use non-sanitation hoses. In severe cases carbon filters can be added inline to the head vent hose to catch the odor before it reaches deck.

On larger vessels the vent can be led overhead to the radar arch, or up a mast. It's possible for the head odor to end up back in the boat due to pressure differences between the deck and cabin.

One solution is to add a second vent line to the holding tank placing the outlet on the opposite of the hull as the other vent hose. (Tip: The larger the vent hose the better it will perform).

Step 6: Inspect the sanitation and pump out hoses and give them a squeeze. If they are soft and spongy or hard and brittle you will have to replace these hoses. Use a clean dry cloth and give these hoses a wipe.

Smell the cloth. If it smells, you have a problem with permeation odor from the hose. This is common with older hoses. The best sanitation hoses only last 3-5 years. (Tip: Wipe test: If you suspect a permeated hose, scrub the hose area clean, wait for several days and then wipe the suspect hose with a damp cloth and sniff the cloth. If it is permeation, the odor will come back soon enough.)

A simple acid flush using a 1 to 20 mixture of Muriatic acid and fresh water of one litre of acid mixed into a 20 litre bucket of water and slowly pumped through the head hoses will dissolve thick residue buildup inside the hoses.

Follow the mixing instructions on the bottle and leave the mix sit inside the hoses overnight. (Note: Hoses with years of neglect may simply collapse thick layers of buildup and accelerate the need for hose replacement). (Muriatic acid is extremely caustic. Use all appropriate protective equipment. Chemical goggles, gloves, and correct respirator).

Step 7: The intake hose and toilet rims of any salt water system are prone to a buildup of micro-organisms that give off a distinct "rotten egg" odor; usually when the head is first flushed after periods of inactivity. Over time this organism can infect the complete head system.

To kill the micro-organisms pull off the intake hose at the inlet and suck up a bleach/fresh water mix (10:1). Continue to pump till the bleach mix has completely filled the inlet hose and the smell of bleach is present in the toilette. Once the bleach is inside the inlet hose let it sit for a few hours before pumping it out. (Tip: Converting to a fresh water flushing system will eliminate this source completely).

Step 8: Check out these other often overlooked odor sources: Dirty bilges - Bacteria and mold growing inside the boat - Gas from leaking fluids on a hot engine and exhaust gasses (repair leaks) - Permeated fuel and oil hoses (replace) - Fish residue & livewells - Refrigerators & Freezers - Upholstery, pillows and carpets - Chain & rope lockers - Sink, grey water & shower and bilge pump sumps - The interior teak/woodwork.

Even though the bilge is mostly dry, it can foster mold and mildew. To clean and freshen the bilge, use Bilge Bath along with a bucket or two of water.

Bilge Bath is biodegradable, but some of the stuff that it looses may not be. It has the odor additive "Odolime" which will knock out the smells, even of diesel and gasoline.

Wash refrigerator, ice boxes, livewells and the inside of the cupboards with Lure & Livewell Cleaner and rinse with water. Pull all the drawers out and inspect behind and below them for any refuse.

Upholstery and carpets can be shampooed with Boat Clean Plus. Pour some into a bucket and use a sponge to create foam. Use a sponge or brush to work the foam into the fabric and then use a wet/dry vacuum to suck up the moisture and let dry. The walls and bulkheads and even the engine can also be washed with Boat Clean Plus and water. Make sure that the surfaces are color fast before washing. Most headliner materials can also be cleaned this way.

Chain & rope lockers get smelly every time the anchor goes up. Take everything out, wipe the locker down with a bleach water solution and air dry it.

Sink and gray water has a distinct stale grease smell. The source may be the gray water tank, the shower sump or often the sink trap. Sink traps hold heavy grease, hair, and other contaminants. The typically recommended method of cleaning the trap is to take it apart and clean the elbows individually.

The interior teak. Wash it with a Murphy Oil and water solution according to the instructions on the bottle. Then use just regular lemon oil to wipe it down again.

Step 9: Once your odor source/s have been identified and eliminated, one more thing remains. Airflow is a must in removing stale smells, open the hatches, install fans, or put up a wind-scoop. Adding an air freshener will add your "favorite odor" but remember, don't use it to mask other odors. All you will get is a wonderful combination of air freshener and sewage!

Step 10: Finally, buy Peggie Hall's book "Get Rid of Boat Odors" - – it's available at Amazon. Although it mostly deals with head odors,– Peggie's nickname is "The Head Mistress". – It also has a small section on making sure you aren't getting bad smells via the bilge.

Plus it tells you anything and everything you need to know about your head and holding tank, including exploded diagrams of several of the most popular brands of heads.

God Bless boaters, we'll see you out there.

Michael McNeil is the owner operator of Bay Pump LLC, which can provide the services for eliminating boat owners described in his article. You can email Michael at en1mac@yahoo.com.


Jul 31, 2010
AquaCat 12.5 17342 Wateree Lake, SC
Not a typo at all if he really means it. ;-)
Jul 1, 1998
Hunter Legend 35 Poulsbo/Semiahmoo WA
Maybe a medical term?

Anyone do crossword puzzles?

Elimination, as in a bodily function. So, .... help with eliminating could mean something else.

A hint is the LLC company - that's often what those in the medical profession use.
Mar 26, 2011
Corsair F-24 MK I Deale, MD
I'm still strugling with the discussion of bleach chemistry. She shouldn't...

I would also advise that a weak washing soda/baking soda/borax solution (http://www.practical-sailor.com/blog/-11249-1.html) is a much better general purpose odor remover and mildew preventative, particularly for fabric and carpets, because unlike bleach, it does not disipate within hours. It will not bleach color. It will bring back muddy, flood damaged carpets (my basement, this spring) when used with a vacuum extractor (or shop vac, in a bind).

But good common sence advice.