Your commercial deep fryer should have a drain valve to allow liquid out. Before you drain your commercial deep fryer, ensure it is switched off and that the equipment and the oil are cool. This prevents burns from hot liquid.
Place an oil transporter or a container with sufficient capacity under your deep fryer to hold the contents and open the drain valve. Wear protective clothing so you aren’t impacted by oil splashing and use a non-slip cleaner if any oil gets on the floor.