I have a Jabsco head on my new B331. It worked great until about a month ago. Now it will not consistantly prime or hold it's prime for water intake on a wet flush. For example, I tried to wet flush this weekend - before actually using the head. I couldn't get it to prime. Thought something might be clogged so pulled the freshwater intake off the pump. No water came out, but when I blew through the line, it was clear. I think this end is above waterline. I then took pump to bowl line off at bowl end and ran water from the sink to fill the line. It primed and worked all afternoon. Before going to bed that evening, it had lost it's prime. Next day, couldn't get it to prime and didn't want to mess with it so used water from sink and dry pump. During one port tack, head on starboard, my daughter used it and reported wet pump worked. I went down and sure enough, it worked. However, it had quit working by raftup time that evening. Sounds like a valve sticks open or shut. I have Peggie's book and have searched the archives, but can't locate exact problem. Advice would be appriciated.