Apr. 1, 2015. TDK Corporation has announced that its Hong Kong-based HDD head manufacturing wholly owned subsidiary, SAE Magnetics (H.K.) Ltd.
You use a wrench to screw, or unscrew a bolt. A screwdriver is for screws. Either way you turn it left. Some bolts have reverse threads and would turn the other way to unbolt.
Unscrew the lock nut above the one you just removed to remove the fill valve. You may need to hold the valve steady inside the tank while you turn the nut underneath through the first few rotations. After you remove the nut, take the fill valve, including the float arm and ball, out of the tank.