It's not necessary to fill the tank to rinse it out...and there's a better way than adding water
through the toilet: At least a couple of times a season--and especially when prepping for winter or other extended layup
, do it a little differently: put a couple of gallons (enough to cover the bottom to a depth
of 3-4") into it via the pumpout fitting, 'cuz that sends the water into the tank at the bottom to stir up any sludge and hold it in suspension so it can be pumped out. Repeat until you only see clean water going through the pumpout sight glass. If you have a macerator or other overboard
discharge pump, put water into the tank one more time and then turn on the pump to rinse out the pump and its associated plumbing
"If you can't explain it to a six year old, you don't completely understand it yourself."