There are several reasons for poor performance of a toilet, but adjusting the water level in the tank often improves the flush. Turning the adjustment screw at the top of the valve on ball-cock valves counter-clockwise increases the water level. Adjusting concentric valves require loosening a small nut at the upper end of the adjustment rod and turning two to three full rotations before tightening the nut again.
Fluidmaster recommends pouring at least a gallon of water from a bucket into the toilet bowl and observing the results to diagnose the problem. If the toilet flushes normally, this diagnostic test eliminates the trap, pipe and vent from potential problems. If the slow flush persists, the problem is in one of these three areas.
A plunger helps to eliminate clogs in the trap or drain pipe. If the plunger does not fix the problem, owners should try a toilet auger. They often find using a plumber's snake or an expansion nozzle on a water hose helpful in eliminating vent problems.
If the test eliminates problems in pipes, traps and vents, there is often a buildup of lime in the toilet. Fluidmaster recommends cleaning the holes under the rim of the toilet bowl with a small screwdriver or the end of a coat hanger along with the use of a commercially available lime dissolving product.