Pressure-fed engines can use fuel stored in non-HP tanks if there is at least some of that fuel type in an HP tank #350
Description
As long as there is 1ml of the fuel stored in an HP tank, the engine can take the rest of the fuel from non-HP tanks.
(image from https://discord.com/channels/319857228905447436/684077440401932290/1348528701255581768)
Relevant conversations:
https://discord.com/channels/319857228905447436/1115321536807718992/1311245293043585044
https://discord.com/channels/319857228905447436/684077440401932290/1364246587408388216
Relevant code according to njits23:
https://github.com/KSP-RO/RealFuels/blob/master/Source/Ullage/UllageSet.cs