A controlled volume of water is slowly pumped by hand into the filter separator sump. If the emergency shut-down system is operating correctly, fuel flow will stop automatically when the level of water in the sump reaches the sensors. This test is performed while the fuel system is operating.

When the test has been completed, and while there is still pressure in the fuel system, the operator opens a drain valve that directs the liquid from the filter separator sump to the bucket (GTP-1787) or to the transparent measuring container (GTP-1799). Any fuel that is drained will float on the water. The operator can then confirm that all of the water that was injected into the sump has been removed.