Almost all older boats, and many boats on the brokerage market, have manual heads. It’s every boat owner’s nightmare, of course, to have a problem with the head, particularly when you’re on a cruise. We’ve all probably tried to fix a clogged or broken head, often with mixed results. Here’s about the best and easiest-to-follow instruction about how to fix a problem with your head:
http://blog.boattrader.com/2017/01/troubleshooting-manual-marine-head.html