Was reading the owners manual and it recommends periodically removing the deck plate and washing down the fuel tank. I've never heard of anyone doing this.
My poly tank gets pretty moldy. A couple times a season I will remove all the pie plates and spray some bleach/detergent mix into the bilge area and on the tank. Hose it all down and pump out the water. I put up all the canvas and leave the plates off so everything can dry out.
once a year while its out for the winter. I pull up the full deck hatch. Clean with soapy water. Let it dry all winter. Reseal the hatch in the spring.