Holding Tank - Depending on use, Pressure wash it once a year if one has an inspection plate. I plan on pressure washing the boat once a year, bottom, thru-holes, bilges ( if necessary) and topsides along with the water and
holding tank. Water tank might not be necessary since I live on the boat and drain the tank once a week.
Water - I use a whole household filters that gets most of the yuck out of the city water supply. I went to Home Depot and made a
rig the attach's directly to the garden hose and my water tank, It lives in my
anchor locker when not in use. Total cost $ 35.00. Price of filters $18 for two. The ends are capped when not in use. It is a pretty cool set-up.