Have you tried to set minimum fuel to 1? I think 0 might be a no minimum setting so you are saying to fill it to brim
Minimum 0 means minimum 0 but newly built ships always get refueled from the building colony and SM'd ships always get free fuel.
I am treating the Harvesters as Stations so I have toggled No Armour (Structural Shell), this is on a save I play with instant build to Identify any issues so these stations are insta-built from the Misc Tab.
I believe when you instabuild a tanker, it will generate with full tanks regardless of min setting. I don't know if this is wai for instant build.
This is WAI, since the only possible exceptions are gas miners and the support tanker(s) that will be assigned to them. Every other ship, including tankers, wants to start fully fueled.
Aurora does not expect you to give orders to Sturctural Shells, only to ships. Building them with no armour severely limits your options for "unit A do this to/with/from unit B."
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Snapto is correct. SM-mode instant build items come complete with full loads.
It is component limited. The 'Transfer Fuel to Colony' order requires a Fuel Handling System component. Refueling Hubs don't count. Armour, engines, and/or Flagging as a Tanker have no effect.