Eliminating head and holding tank odors is a common topic on sailing forums. At the root of the problem is an imbalance between the good (aerobic) bacteria and the bad (anaerobic) bacteria. Aerobic bacteria break down waste without creating strong odors while anaerobic bacteria create strong sulfur odors to which most of us object. The solution is to provide enough oxygen to the aerobic bacteria so they can live well and prosper, dominating the anaerobic bacteria. 

One effective method is recommended by Peggie Hall, author of Get Rid of Boat Odors is increasing the size of the tank vent and using Raritan’s K.O. According to Raritan’s website, K.O. uses “live, odor-killing bacteria which digest liquids, solid waste and paper, totally emulsifying them.” That coupled with increased oxygen flow from a larger vent helps to reduce holding tank odors.

For many years I used K.O. with modest success. Of course, when I replumbed the holding tank on Identity Crisis I failed to follow Peggie’s advice with a larger diameter vent, so that may account for its limited effectiveness.

The odor problem continued on Second Star even after replacing all the sanitation hoses. Due to the holding tank placement, installing a larger vent was not easily accomplished, and as with tasks of this nature, it never seemed to rise to the top of the To-Do list. Now, it may never reach the top of the list. The reason, Zaal’s NoFlex Digester.

Last summer (2019), figuring we had nothing to lose, we gave NoFlex Digester a try. And, it simply worked. I was skeptical at first as it seemed to make no difference, however over the course of the 12-day cruise odors became less and less noticeable. By the time we pumped out for the last time, there was little or no odor.

According to the Boater’s Mate website, NoFlex Digester is “a powerful and effective oxygenator. It does not utilize any harsh, harmful chemicals, no enzymes, no deodorants, no biocides, no nitrates or formaldehyde.  Its proprietary formula creates cleaning oxygen immediately reducing sludge and odors.” While there may be some marketing hype in the claim, adding oxygen to the holding tank supports the basic science of fostering aerobic bacteria growth which retards anaerobic growth.

I’m sold. It works. Good bye Raritan KO, hello Zaal’s NoFlex Digester.


The Safety Data Sheet is located here: https://www.gemini-ltd.com/pdfs/Extras/SDS-2017-Noflex-Digestor.pdf

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