in most gasoline powered lift trucks the fuel pickup tube is located on the same component as the sensor mounted on top of the tank. If your wanting to know how long the pickup tube is it generally is as deep as the tank is on top mounted units with probably a 1" gap between the tube and the tank bottom.

If not there then it could be along the inside wall of the engine compartment near the base(on same side as tank of course), those type units you can trace the fuel hose from the carb to the pump, to fuel filter and down to the tank feed outlet line.