Most commercial toilets are one-piece units without an integral tank. Direct water pressure from the supply line, controlled by the manually operated flush valve and metered by a control stop screw, provides the flushing action. The handle and flush valve body are a separate, heavy-duty unit plumbed to the water supply line just above the top of the toilet body. Flushing pressure can be altered by adjusting the control stop screw inside the valve body.
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Unscrew the access cap located at the elbow where the water supply line enters the flush valve. This will expose the valve control stop screw.
Rotate the control stop screw counter-clockwise with a screwdriver until it is fully open. Rotate the control stop screw clockwise to fully close the valve.
Rotate the control stop screw counter-clockwise, one-quarter turn at a time. Test flush the toilet after each quarter turn of the screw to evaluate flushing pressure. Continue to open the control stop screw in one-quarter turn increments until adequate flushing volume and pressure is observed. Reinstall the access cap.
Check the building water pressure if adjusting the control stop screw does not produce adequate flushing pressure. Water supply specifications for a typical manual commercial toilet flush valve such as the Kohler K-13517 call for a static pressure of 35 pounds per square inch and a flow of 25 gallons per minute.