Description of the issue:

As with #4533, #2655, #2412, and #2260, recipes that call for a bucket of fluid (in this case, Water) do work with a bucket of the fluid in the inventory. However, they will not use fluids added to the internal tank.

Versions & Modlist

https://pastebin.com/bxi33jLk

Yes I am aware that both Forge and IE (and IP) are a version or two behind. Unfortunately, updating Forge or mod files is a last result, if that's the issue, given that this is a dedicated server that would need to be shut down for an extended time to do so.

That said, knowing the next version up still seems to have this issue, I'd just chalk this down as a notification of an issue, rather than support being needed. Personally, I've used a bottler to get around the issue for the time being.

This issue appears to persist with the most recent version as well.

Then file a proper report.