One of the most underrated RV features, a black tank flush is a hose port on the RV that essentially allows you to power wash the inside of your black tank. After emptying the black tank, connect a hose to the black tank flush port and spray water into the tank, giving it a good scrub and preventing waste buildup. You should always follow a black tank flush by immediately putting fresh water and chemicals into the black tank. Make sure to have a dedicated hose for flushing the black tank and never use your fresh water drinking hose to do the dirty jobs.