From a long discussion with NathanKell: How to make new tanks and/or make parts use MFT tanks First you need a TANK_DEFINITION, which has the following fields: name = the name of the TANK_DEFINITION. basemass = modifies the dry mass of the part. Use a value to replace the part's mass, like 0.01. Add " * volume" after the value to make it depend on the tank volume, like "0.0002 * volume". Or use -1 to leave the part's mass alone. One or more TANK blocks. TANK has the following fields: name