Feed the connecting lead/s and the threaded portion of the water float switch through the hole in the container , from the inside. Take care to ensure that the sealing washer/gasket is not damaged and that it is correctly positioned against the face of the tank wall and the collar of the water float switch.
Feed the fixing nut over the connecting lead/s and position on the float switch thread, ready for tightening.
Hold the float switch firmly, ensuring that the orientation of the float is correct and that the sealing washer/gasket is not impaired, and tighten the nut, until water float switch finger tight.