Or an even simpler way is to keep a quart container in the head and fill it with fresh water and dump into the head when you want to flush. I have an advantage in my P-33-2 in that the head is aft and the sink is very close to the ice box. As the ice melts, there's a hand pump
in the head sink to empty the water out of the ice box. So, when using the head, I either pump
water from the ice box into the container to pour in the head, or I use the pressure water system (the faucett in the head is one of those telephone jobs) and pour the fresh water in that way. Keeping the Ches Bay water out of the holding tank
goes a long way to hold down odors.