Sounds like ball is dragging against seal
Turn off water supply
Hold ball OPEN via foot pedal
Using your hands rub/flex seal cleaning any scale/crud off top/bottom sing some dish soap
Clean top of ball surface also
Rinse seal top/bottom and ball to remove soap
Then rub seal top/bottom with olive oil using your hands...closing/opening ball
Ball should close smoothly and hold water
(ball drive is on backside of bowl and has no adjustments)
https://www.thetford.com/part/aqua-magic-style-plus/