Jabsco backup

[beilts]

I put a new Jabsco manual head in about 2 years ago. Worked great. After my last trip (during which I had a pump out) it started backing up with waste water. I pump it dry, turn to 'lock' and fills up again. Never overflowed.
Best guesses..........does it need a new joker valve already? is the tank actually full again ( I doubt it, but maybe so) and causing a backup?

 

[kappykaplan]

Yep, you need a new joker valve. I had to replace mine this year - two years after I installed the new head. Some say joker valve should be replaced annually.