First you need to make sure seal is clean. That means using your fingers to go completely around seal top/bottom/sides checking for deposits/tears flexing it while you check.
Then using your fingers coat the seal thoroughly with good lubricant (NOTHING petroleum based ---- olive oil or pledge furniture polish is GOOD)
Also clean ball top and edges ...... lubricate
Add water to bowl.
If it drains out ...... tighten band clamp (minor adjustment)
Check ball open close function
Repeat until ball open/closes and water remains in bowl