I'm posting this because I just finished trouble shooting a problem with my Jabsco electric head which would not flush properly. It has been a slowly developing issue for nearly a year and I assumed it was the hoses getting filled with calcium. It was not.
The problem began in Fiji when we noticed that it would fill with water and only slowly empty the bowl through the maserator. This eventually the flushing process got slower and slower until it simply stopped emptying the bowl leaving one with a really nasty problem.
So, I finally broke down and took the entire head apart and removed all the hoses to find the hoses were pretty clean and all the seals were in good shape. So what was the problem?
There is this little thing called the "Joker Valve" which is essentially a one way valve shaped like a 3 pointed star. It is somewhat hidden in the exhaust line. Well, apparently calcium can build-up on the backside of this valve and prevent it from opening and closing. I am assuming the problem started when we left our boat on the hard in Fiji and the lines dried leaving the valve encrusted.
If you are having problems with your Jabsco head not emptying when flushing and all else seems to work just fine, the problem might very well be the joker valve needs to be cleaned or replaced.
Hopes this saves someone a lot of time and effort, because I couldn't find anything on the web while I was pulling my hair out