For ongoing maintenance try using white vinegar and cheap oil - vegetable, corn, etc. (ie. not petroleum products). Once a month fill your head with fresh water and add 3 or 4 cups of vinegar. Pump the head a few times to get the solution spread through the system (about 1/4 should remain in the bowl). Let it sit for a few hours before flushing it out. Afterward add 1/4 cup of oil and repeat the process of pumping the head and waiting a few hours.
This process will clean and lube the head and reduce your maintenance by half. After living aboard and maintaining our own sanitation system for 10 years, we can guarantee this process works. Best of all it's good for both the environment and your wallet.