allow its return in a liquid state this can be effected by mounting the vessel 590 with the entry port at the bottom or by using a fill drain tube within the vessel not shown or other means the storage and return process capacity is improved for a given vessel 590 size and working pressure limit by allowing the liquid to return to the containment system 300 in liquid rather than vapor form which would take up much more space porting from the vessel 590 top would allow complete evaporation of the liquid as the pressure drops back near ambient atmospheric pressure levels some evaporation may occur even when liquid is fed to the drain valve 570 depending upon the stored liquid temperature due to the large pressure drop which occurs when the liquid is returned to the containment system 300 an optional pressure regulator 575 can be included in the drain piping in series with the drain valve 570 to regulate and limit the pressure of the draining liquid and or vapor to prevent excessive pressures in the single connecting pipe 555 and any part of the fuel storage containment system 300 during the draining period when or if the fuel storage containment system 300 pressure increases above a fourth predetermined threshold of approximately u2212 0 2 u2033 wc decision 1018 the controller 510 deactivates the solenoid operated drain valve 570 which halts the flow of liquid or vapor and air back into the containment system 300 preventing further increase in containment system 300 pressure and leaving it at a reasonably low level step 1020 additionally since the storage vessel 590 may drain completely before the containment system 300 pressure reaches the fourth threshold a predetermined.