As soon as you change the fluid level percentage after pumping it in the Reaction Chamber you get this message spammed constantly in the console:
[main/INFO] [STDOUT]: [techguns.client.render.tileentities.RenderReactionChamber:drawFluidCubeWithTesselator:231]: Height:0.29375 MH:2.9375

The spam stops as soon as you void the input tank, thus disabling the rendering of the liquid.
Tested on Techguns version 1.12.2-2.0.1.1 and Forge 14.23.2.2613