empty tank
Mix the bleach, with water, into a one-gallon container and pour it into the fresh water holding tank. Fill the fresh water tank almost completely full of potable water. Turn the water pump on, open all hot and cold faucets and run the water until you smell the bleach at each faucet. Close the faucets.
The amount of bleach depends on the size of water tank . If you dont know, add one quarter to one gallon then pour in tank and add water until full. Disinfection takes time (several hours) so let it sit and or go for a boat ride or trailer it around. Maybe needs to repeated at first then every season.
At end or year empty tank or keep it empty then fill before trip and empty afterwards
This is basic info