Additives Fight Urine Odor

Nilodor urine digester surprises testers with two days of odor suppression.


Some will claim urine is sterile and doesn’t smell. Horse hockey. No matter how careful you are, urine is loaded with nitrogen (urea) and potassium. Bacteria will find their way in, and the potent brew will ferment into a nasty solids-laden syrup within a few days.

Unlike a holding tank, where the purpose of treatments is to support a healthy biome, the best urine treatments are like those used in portable toilets to stop bioactivity dead. Urine treatments modify the urine chemistry so that fermentation cannot take hold and any ammonia that is generated will be retained in solution. They really work.

Like holding tank or portable toilet treatments, the greater portion of the treatment is added to the tank before use. However, just as we recommend spraying a diluted odor treatment in the bowl of holding tank-type heads (see PS June 2017, “A Simple Solution to Toilet Bowl Stink”), the urine diverter can also benefit from a light spray of urine treatment after each use to prevent the build-up of scale and stains and to prevent odor from the funnel surface itself.

Dilute as recommended. Add a little Febreeze or other odor neutralizer if you like. Nilodor includes a mild fragrance and citric acid has a barely noticeable citrus odor.

Never add bleach to the urine container. The hypochlorite will react with the urea, creating dangerous amounts of chloramine gas.


Sugar, white vinegar, CLR (lactic acid), citric acid, Wet-And-Forget, and Nilodor’s Urine Digester.


Sugar, vinegar, and Nilodor doses were based on manufacturer and user suggestions. Lactic and citric acid doses were based on equivalent morality (a measure of capacity) to vinegar. We exposed the test bottles to the air for two days to inoculate them with ambient bacteria and then sealed them up for another five days, checking them for odor every two days. We also tested them as sprays to keep the funnel clean and odor-free.


Fresh urine has a relatively mild smell, which was slightly reduced by sugar and eliminated completely by the acid products and Nilodor, with citric acid and Nilodor in the lead. Acids reduce the volatility of alkaline gases, including ammonia and trimethylamine, which are generated during the breakdown of urine, by converting them into nonvolatile forms which stay in the water. The pH is also reduced enough to inhibit fermentation. Nilodor uses enzymes.

All of these are nontoxic to the environment, biodegradable, and will not interfere with urine disposal.


ITEM -- Cane sugar White vinegar Citric acid CLR Moss, Mildew, and Algae Stain Remover Urine Digestor Deodorizer 
ACTIVE INGREDIENT -- Sucrose Acetic acid Citric acid Lactic acid Benzalkonium chloride Enzymes Benzalkonium chloride 
CONCENTRATION (%) -- 100% 5% 100% 25% Not listed 2% 
$ PER GALLON -- $4 -- $22 $30 $28 $21 
$ PER POUND OF ACTIVE INGREDIENT -- $1.30 $9.41 $15 $10.35 $14.11 -- $9.88 
OUNCES / GALLON -- 4 oz. 4 oz. 0.5 oz. 1.2 oz. 0.5 oz. 2 oz. 2 oz. 
TEST DOSE g/ml -- 3.1g/ 100 ml 3.1ml/ 100 ml 0.5g/ 100ml 0.93ml/ 100ml 0.39ml/ 100ml 1.55ml/ 100ml 1.55ml/ 100ml 
ODOR (2 DAYS) Bad Strong Barely noticeable* None None None None None 
ODOR (7 DAYS) Very strong Awful Very noticeable Noticeable Noticeable Noticeable Noticeable Noticeable 
$ / GALLON OF URINE TREATED -- $0.33 $0.13 $0.47 $0.40 $0.12 $0.44 $0.33 


The idea is that like making jelly, if the solution is strong it will stop bacterial action. The actual result was cloudy urine, a bacterial scum formed on the surface, and after a few days, and a horrible skink far worse than if we had done nothing at all. We tested 1/2 cup/gallon.

Bottom line: This experiment stunk.


By adding a few inches to the bottle before starting, the pH is lowered enough to prevent fermentation. In practice, we could still smell the vinegar, but not much else. A favorite among users and manufacturers, it is economical and widely available. (1/2 cup/gallon of holding tank)

Bottom line: Traditional, effective, and the Budget Buy.


For the first few days it is slightly more effective than vinegar, but if you leave the urine in the bottle for more than three days then the vinegar takes a slight lead. It is better at cleaning the bowl, and it requires less storage space because it is a dry powder; a 5-pound bag has the same effectiveness as 4 gallons of vinegar. (2 tablespoons/gallon of holding tank, or 1 teaspoon per pint to use as a spray)

Bottom line: Recommended.


As the PS choice for best descaler we thought it had a good chance. It did kill the smell at first, but it created a fine precipitate in the jar and the smell got worse after three days. (3 tablespoons/gallon of holding tank or 1 teaspoon/pint to use as spray)

Bottom line: A good choice for cleaning the diverter, but not as a sole treatment.


A popular brand for home cleaning Wetand- Forget has the same active ingredient as Odorban, but five times the concentration, making it the least expensive source of BAC we know of.

Performance was similar to Odorban. Use a ratio of 1 tablespoon per gallon of holding tank, or 1 teaspoon per pint of water to use as a spray for cleaning or fighting surface odor.

Bottom line: This is not a good choice for this particular use.


Testers detected no odor for the first two days, only the mild fragrance of the product. For the next 7 days it remained mild, less than vinegar and citric acid, and orders of magnitude better than raw or sugar-treated urine. It has half the storage space of vinegar. (1/4 cup/gallon of holding tank, or 1 tablespoon/pint to use as a spray.)

Bottom line: This is our Best Choice for odor control.


C-head suggests this formula (1/4 cup Odorban/gallon of holding tank, or 1 tablespoon Odorban/pint to use as a spray) for spraying the its urine diverter. It is based on benzalkonium chloride (BAC), a chemistry we have found effective on many mold and odor problems around the boat. We didn’t find it as effective as other products in fighting urine odors.

Bottom line: Recommended by CHead but we were less impressed.


Except for sugar, all of the treatments were quite impressive for the first few days, and there is really no reason to leave it longer than that.

After 7 days it was less than pleasant to stick our noses in the jars, but still several orders of magnitude better than the rip-your-nose-off stink of non-treated or sugar-treated urine. We recommend spraying down the urine diverter after every use to keep it clean and to supplement the initial treatment. Just keep the spray out of the solids bucket.

Drew Frye
Drew Frye, Practical Sailor’s technical editor, has used his background in chemistry and engineering to help guide Practical Sailor toward some of the most important topics covered during the past 10 years. His in-depth reporting on everything from anchors to safety tethers to fuel additives have netted multiple awards from Boating Writers International. With more than three decades of experience as a refinery engineer and a sailor, he has a knack for discovering money-saving “home-brew” products or “hacks” that make boating affordable for almost anyone. He has conducted dozens of tests for Practical Sailor and published over 200 articles on sailing equipment. His rigorous testing has prompted the improvement and introduction of several marine products that might not exist without his input. His book “Rigging Modern Anchors” has won wide praise for introducing the use of modern materials and novel techniques to solve an array of anchoring challenges. 


  1. I spray one or two pumps of Clorox all-purpose cleaner in the bole after each flush it contains Sodium Hypochlorite 1.84% and the average human contains “Levels of ammonia in the blood of
    healthy humans range from 0.7–2 mg/L” this alone gives me a great comfort level that no significant levels of “toxic gases called chloramines are produced” but in addition, we need to account for the saltwater sucked into the flush of the head further leading to the dilution of aforementioned chemicals.
    the bottom line is my head always smells frech and I have had no ill effects thus far.
    It took me a while to find a solution to the smell in the boat from the heads.
    I am not a chemist or a physician or a toxicologist if you believe I am endangering myself or others with this practice please reach out to me with further information.

    The reason I did the recherche was the article said “Never add bleach to the urine container. The hypochlorite will react with the urea, creating dangerous amounts of chloramine gas.” scared me.

  2. We have used a Nature’s Head composting head as live aboard cruisers since 2016. While there is more labor involved in maintaining this than in dealing with a holding tank system, we love the extra storage aboard created by no holding tank and also the idea that we never discharge overboard, except…

    There is the urine. I am wondering if any of the additives you tested are effective in reducing the nitrogen level in the urine? While we always try to empty our urine jug into a land side toilet, there are those times when that isn’t practical. Assuming the major water pollutant in our urine is the nitrogen, I am always exploring ways to remove that from the liquid. As a gas, I judge it as a non-pollutant. BTW there is more nitrogen in our urine that in our feces, just sayin.’

  3. You need to include both urea (named for urine, because it is prevalent there) and ammonia in the calculation of the reaction with bleach, since bleach will react with both (urea is an ammonia salt). Urine typically contains about 500 ppm urea, still only 0.05%. We added bleach to fresh urine samples, they bubbled in reaction, and so it seemed like a bad idea to us. You have made the urine far more toxic to the environment, something we can see no reason to do. Sewage treatment plants are forbidden from post chlorinating until the ammonia is removed. However, you are correct, the risk to you is quite small.

    You can’t remove nitrogen by any simple chemical chemical addition. It’s an element and it is there until it is physically removed, either plants or advanced sewage treatment processing (conversion to nitrate followed by anoxic denitrification).

  4. Thanks for the article. I’m sure it was the spellcheck, but thinking it’s molality not morality.

    Like stated above, from a practical point we’re not always able to empty urine on shore. While urine is sterile in your bladder, urine in the container is obviously not. But from an environmental standpoint, I don’t think of them as pathogenic like fecal chloroforms. Eutrophication risk seems insignificant if you avoid lakes, estuaries, and harbors.

    Niloder states “safe around kids and pets”. Curious if the use of Niloders “selected strains of natural bacteria (bacillus), enzyme cultures, and odor neutralizer and surfactants” changes the thinking about the occasional necessity of overboard urine container discharge.

  5. Spell check makes fools of us, and them we miss them during editing! Yes, molality. I have added that to my WORD dictionary.

    Regarding discharge, there’s just not enough information to answer knowledgeably. The few times I have needed to empty it in a remote area, I walked into the woods 25 yards and poured it into the rotting leaves. The usual backpacker practice. I also use citric acid most of the time; I know what that is. Personally, I dislike the smell of vinegar.