If you have an Atwood water heater this might help. It is from the Atwood water heater manual for treating the aluminum tank itself and not the entire water system. The aluminum tanks can get a bit funky sulfur smelling. I don't believe it is necessary for the suburban tanks since they are porcelain lined. The instructions says to remove the water heater relief valve and pour the solution into the tank through the opening. This is probably not necessary if you use the winterizing connection to fill the tank. You will also need to lift the lever on the relief valve to allow the tank to fill completely.
FLUSHING YOUR WATER HEATER TO REMOVE
THE ROTTEN EGG ODOR
1. Turn off your main water supply. Drain you water heater tank. Reinstall drain plug. Remove the pressure-temperature relief valve. With a funnel use 4 parts white vinegar to two parts water. (In a 6 gallon tank that would be 4 gallons vinegar to 2 gallons water).
2. Cycle the water heater, letting it run under normal operation 4-5 times. At no time do you remove the vinegar from the tank Once this has been completed, remove the drain plug and drain the water heater.
3. After thoroughly draining the tank, to remove the sediment, flush the water heater.
If you elect to use air pressure, it may be applied either through the inlet or outlet on the rear of the tank or applied through the pressure-temperature relief valve. Remove the pressure-temperature relief valve and insert your air pressure through the pressure-temperature relief valve coupling. In either case, with the drain valve open, the air pressure will force the remaining water out of the unit.
If air pressure is unavailable, your unit can be flushed with fresh water. Fresh water should be pumped into the tank either with the onboard pump or external water pressure. External pressure may be hosed into the unit either through the inlet or outlet found on the rear of the tank or the pressure-temperature relief valve coupling located on the front of the unit.
Continue this flushing process for approximately five minutes allowing ample time for the fresh water to agitate the stagnant water on the bottom of the tank and forcing the deposits through the drain opening.
4. Upon completion of the steps above, replace the drain plug and the pressure-temperature relief valve.
5. Refill tank with fresh water that contains no sulphur.
The Atwood water heater is designed for use in a Recreation Vehicle. If you use your vehicle frequently or for long periods of time, flushing the water heater
several times a year will prolong the life of the storage tank.