What year KK42? Our water tanks (2-150 gallon each), has a ~6-8” ss inspection port on the top of the rear section of the tank. Ours is under the hanging locker’s floor in the guest stateroom. Once a year I empty the tanks and take a high velocity nozzle on a garden hose, blast the inside, drain and repeat till they look clean. Other than that, we haven’t done or do anything else in 12 years. We do filter all the water that goes into the tanks other than from the water maker. We also live on and cruise full time so the water gets turned over regularly.