I'm making a mod with faster trains, and wanted to add compatibility with your mod by adding a faster version of the diesel train. Problem is, I can't figure out how to get the train to intake the fluid. It's already a copy of yours with changed stats, so it uses the fake items. I have entered it into remote.call with this:

remote.call("Diesel-Locomotive_loco_tank_pair_list", "add_loco_tank_pair", "Diesel-Bullet-Train", "Diesel-Locomotive-fluid-locomotive-proxy-tank-")

but it still doesn't intake the fluid. I checked, and the valid fuel type is indeed correct. This remote.call is being run in the same places as yours as well.
Do you have somewhere else I need to interface my locomotive?

Hey, sorry for the delay. Been busy with work and family, and have been fighting allergies at the same time. Ugh.

I've been thinking through this and the only thing that I can think of that could be preventing the fuel intake is if there's a filter set on the tanks. Make sure that in your settings -> mod settings in the game that the allowed fuel types is set for "both heavy & light". This will prevent it from creating a filter on the tanks.