I am assuming the drip is in the cistern and the ball valve is the plastic type.
Try adjusting the valve adjuster pin on the valve end of the ball arm. I'ts a threaded pin that pushes against the valve pin to close the water off when filled.
Release the locknut and turn the pin [has slot in end for screwdriver] clockwise 1 to 2 full turns and see if that stops the drip.[It turns the water off sooner]re tighten lock nut.
If not the ball valve washer could need replacement.
To replace. Turn off the water feed to the cistern and on the inside of the cistern at the valve end of the float/ball valve arm is a split pin, remove this pin and take the arm off of the valve. Unscrew the cap end on the valve this reveals the washer usually a large black rubber disc. Replace the washer and replace the end cap [make sure the valve pin is in place in the cap]. Replace the arm and it's split pin. turn on the water and when full you shouldn't hear any dripping noises.
If it's the toilet pan driping from the cistern then you may have to have the syphon replaced.
Bob, January 2005
