be pressure operated is disposed in the vapor dome under tank wall portion 24 as denoted by reference numeral 52 the vent valve 52 has an outlet which is connected through conduit or hose 54 to the outlet 42 of vent valve 38 the conduit 54 passes under the lowest level section 28 of the tank upper wall and conduit 54 has a drain valve indicated generally at 56 disposed therein and located under the lowest section 28 of the upper tank wall as shown in fig1 referring to fig3 the drain valve 56 is shown in one embodiment having a body 58 with an annular outwardly extending flange 60 formed adjacent the upper end thereof which flange is secured to the conduit 54 by snap locking within an annular receptacle 62 preferably formed internally with a portion of conduit 54 and sealed by labyrinth seal 64 the body has a valve seat 66 disposed therein which communicates with the interior of the conduit 54 via flow passage 67 a float 68 is slidably disposed within the body and has a flexible membrane valve member 70 provided on the upper end thereof for contacting and closing against valve seat 66 upon the fuel level in the tank rising to the level of the lower surface of the lowest portion 28 of the tank upper wall membrane valve number 70 is partially attached to the float 68 about support 69 on the float and a centrally located curved surface 71 makes contact with the undersurface of valve member 70 to urge the central region thereof into contact with the valve seat 66.