This quick fix is for the bestway sand filter pump 58126 and 58199.

In most case, the leaking from the control valve is because the washer (black O-ring rubber) is not at right position, you can follow the following step to fix it

Firstly, Unscrew the control valve from the rest of the pump as below:

Secondly, one person press down the round cover using hands, another person uses screw driver and hammer to detach the control valve handle as below:

Then, remove the round cover, you will see the washers, which are black O-ring rubbers, please check and make sure they are in right position

At last, undo all the steps as above to put back the control valve, the leaking should be fixed now