With careful monitoring and pre-filtering of dockside water and pre-filtration, this procedure should only be required once annually or less frequently. Regular inspections—and a proper mix of winterizing glycol—will prevent future problems.
First the tank needs to be clean. Look inside with a flashlight; is there any sediment on the bottom or scum on the walls? Feel the walls; are they slick, evidence of healthy bacterial growth? It all must go. Hopefully there is reasonable access, for there is no substitute for a good hand scrubbing and rinse-down with a high powered hose. Machine dishwasher detergent works well as do long handled brushes. A power washer can help, but some angle fittings will be needed and it won’t do the job by itself. Once you’ve taken care of any growth, the next step is sanitizing.
There is a standard sanitizing procedure for recreational vehicles (ANSI A119.2 section 10.that works just as well for boats. We’ve added a few details, but the bones of it come straight from the code and have been reviewed and accepted by the U.S. Public Health Service.
Turn off the hot water heater until finished.
Remove any carbon canisters or micron rated filters. Remove any faucet aerator screens. Wire mesh pump protection strainers should stay in place. The plumbing will very likely slough off a layer of bacteria during later flushing steps.
Clean and remove the vent screen and flush the vent hose.
Use either following methods to determine the amount of common household bleach needed to sanitize the tank.
A. Multiply gallons of tank capacity by 0.13; the result is the ounces of bleach needed to sanitize the tank. This is 1/8 cup of plain bleach (no fragrance) per 10 gallons.
B. Multiply liters of tank capacity by 1.0; the result is the milliliters of bleach needed to sanitize the tank.
Mix the proper amount of bleach within a 1-gallon container of water. This will provide better mixing and reduce spot corrosion of aluminum tanks.
Pour the solution (water/bleach) into the tank and fill the tank with potable water.
If possible, allow some solution to escape though the vent. (If the vent is exterior, prevent any spillage into local waters.) This will sanitize the vent line.
Open all faucets (hot and cold) allowing the water to run until all air is purged and the distinct odor of chlorine is detected. Leave the pressure pump on.
The standard solution must have four hours of contact time to disinfect completely. Doubling the solution concentration reduces the contact time to one hour.
When the contact time is completed, drain the tank. Refill with potable water and purge the plumbing of all sanitizing solution. Repeat until bleach is no longer detectable.
