Fluid selling stations have a flaw preventing gas from escaping from their internal selling tanks.
the steps to replicate:
a dynamic tank (12900 Liters is the size i had on my mini tug) with a pump pumping air into the tank to prevent the evacuating Fluid pumps from pulling vacuum( otherwise the transfer rate drops till it eventually reaches 0 )
A pump to pump the tanks contents out to the selling station (in this case i recommend not using a fluid relief valve as filtering the contents is something a new player may not understand needs to happen at a station they believe will only take diesel)
if i have explained the reproduction correctly, the selling station tank will eventually be filled with air, and the selling station will be unusable for air.
remedy the situation i would recommend adding a pressure relief valve to the selling points, or perhaps a fluid relief valve to the outlet side of the two large pumps inside the selling station to prevent them from taking in air.