I just added experimental support for tender wagons in version 0.18.4
The feature is disabled by default, can however be activated in the map mod settings.
By default fluids can only be drawn from the first wagon behind a continuous chain of locomotives all pointing in the same way. This wagon will provide fluids to all locomotives in that chain that use the same fluid.
Fluids will not always be drawn when the locomotive is standing still (limitation of the current code) and will only be drawn if at least 1 unit of fluid is in the locomotive (another limitation of the current code). Also by default fluids are only drawn in batches of at least 100 units.
Hope you like it.