Not a major bug but it seems that the fluid part of the hydratator is anchored to the left of the window instead of within the boundaries of the tank GUI.

Forge : 1.12 - 14.21.1.2443
StevesCarts-1.12-2.4.6.36
RebornCore-1.12-3.2.5.88-universal

The cart was created with the creative upgrade of the cart assembler.

The bug persist even when selecting other GUI size options in the minecraft options.