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treatment fluids for pump out toilet holding tanks

Can you give me any advice about the various treatments and products available for a pump out toilet holding tank? What are their various merits and/or problems. What is everyone out there using currently?

Asked by: heather dawes  | 9.21pm, Wednesday 11 December


WW says:

There are a number of treatment options, from the "do nothing" to the "kill everything in the tank" versions.
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A lot of what you can do depends on what has been done before- if an older tank has been routinely used with older, blue, formaldehyde products, then adding other treatments may be pointless, as many will not work.
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If you change treatments, then a thorough clean and flush (to remove the sludge as well) from the tank is imperative, as many treatments don't interact.
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The "do nothing" approach is not to be generally recommended, as it can lead to pathogenic microbial activity developing- and when you (or a boatyard) empty the tank, the aerosol produced (which can be invisible) will contain droplets of untreated sewage, which can be breathed in, and cause issues...
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Some of the biological treatments work well if there is a good flow of air through the tank, although this is often a "suck it and see" approach, as what works well for one person, may not for another. some are designed more for smaller (Porta-Potti) sized tanks, and so over more than 4 days, greatly lose their effectiveness- you need to choose one that is for longer term use.
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considering your holding tank useage as well is important. A residential boat, which empties more frequently that one used occasionally will have different requirements. If the boat is tied up, then sludging is a problem, more than a a boat used on moving water, such as a river, where the tank contents are regularly sloshed about!
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some of the biological treatments require regular dosing to remain effective and this can be prohibitively expensive. There are also ones which release oxygen, to help aerobic decomposition, but, again, this only works for a period of time before activity stops. Some microbial mixtures work well, but better in some tanks than others.
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Some of the biological treatments do not respond well to many toilet cleaners (and certainly never, ever bleach!) so sticking with products such as Ecover toilet cleaner are probably best. Highly acidic cleaners (or strongly alkaline)can also upset the pH balance of the tank and render any microbial action inneffective.
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The next set of treatments are those that inhibit microbial action, but are biodegradeable- a half-way house between those that actively break down waste (such as the claims of many bio treatments) and those that prevent microbes from flourishing. Some of these are quite effective in small doses, and remain active for weeks even in large tanks. they are effectively "green versions of Blue". Some are better than others, with some aimed at the larger holding tank size.
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Lastly are the traditional formaldedhye (methanal) and methanol based "blue" treatments (which may not always be blue). These, in the UK, are the only treatment that has a British Standard. They are designed, in the short term at least, to stop all microbial activity, to reduce the chance of infection, rather than break down the waste completely. They have been used for years (before WWII) because, to a greater or lesser degree, they work.
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However, they are not nice- formaldehyde (methanal) and methanol are easily absorbed through the skin and mucal membranes, and are considered possible carginogens. In larger amounts they can wipe out the fauna of small toilet works and certainly damage septic tank systems. The toilet industry tend to avoid these now, aiming for safer alternatives.
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Experimentation is often the best route. If your tank has decent (oversized) air vents (or even have an air pump system, which pushes air through a diffuser- like in an aquarium) then biological systems which required oxygen (aerobic conditions) may work very well. You can put a charcoal cannister filter on the exit pipe to avoid smells- which should be minimal if the microbes are working in an oxygen rich environment. Sulphurous gases and methane are only produced in low-oxygen (anerobic) conditions.
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If your tanks is not well ventilated, then you may be better with a biodegradeable biocide. However, start with a biological system, then move to a biocide, if you cannot get the system to work.
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what works for one boat doesn't often work well for another. Useage pattersn, amount of solid/liquid waste, concentration of waste, amoung of cellulose (toilet paper) loading, frequency of emptying, size of tank, location (warmer tanks help decomposition) air change rates, all effect how well a treatment works.
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Long answer above, but the short one is- you will have to try for yourself! Just avoid traditional blue. Start with biological treatments for larger tanks.
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If you are designing a new boat, or fitting a new holding tank, then contact me on m.langley@waterwaysworld.com and I may be able to supply some ideas for a holding tank and treatment system that will work very well.
Regards,
Mark

Mark Langley  | 12.17PM, Thursday 12 December

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