(This is the same reply I posted to this question in the trawler
should be at least nominally rinsed out after every pumpout or dumpout...thoroughly flushed out 2-4x year depending upon length of your season, and especially in preparation for winter or any other extended layup
. It’s not hard to do, and all you need is water:
Pump out the tank, or dump it at sea. Then put enough water into the tank via the deck
pumpout--becasue that sends the water into the tank at the bottom to stir up any sludge and hold it in suspension so it can be pumped out--to cover the bottom to a depth
of 4-6”... it can be fresh water at the dock
or sea water using a washdown pump. Pump out or dump... repeat...repeat...repeat...till you’re pumping or dumping clean water.
Human body waste contains animals
fats which can build up on tank walls and clog tank gauge senders. So every year or two--or any time you’re preparing the boat for winter or other extended layup--it’s a good idea to clean out the tank. Follow the above instructions, then fill the tank with clean water and put a gallon (2 gallons if the tank is 50 gallons or larger) of liquid Tide, Wisk or any heavy duty liquid detergent and about 10 lbs of ice cubes into the tank via the deck
pumpout fitting (not down the toilet!). Use “homemade” ice, not bagged ice...”homemade” cubes are larger and harder, so they last a lot longer. Go sailing and tack a lot, or go out on a day when seas are bit rough if you’re a power boat
. Then, if you can, let it sit overnight. Pump out and also run some of the detergent solution through any macerator pump and related plumbing
. Fill tank again with clean fresh water...pump out or dump and rinse out again.
Chemical holding tank products are cheap
, but they don't work and they're about an environmentally UNfriendly as it's possible for anything to be. I suggest you try a product called Odorlos. Odorlos
The active ingredient is nitrates which help to promote oxygen release from the waste (oxygen is key to odor
elimination). It's a lot more readily available --not to mention a lot less expensive--from RV supply stores than marine
Never use bleach in a sanitation system because it's destructive to rubber and breaks down hose resistance to odor
Vent line filters should only be used as a last resort because a) they actually help to create the problem they're sold to solve...and b) they're EXPENSIVE!