There used to be four issues for this, but Github lets us make these checkbox thingies now:
[ ] Add a normal renderer: the special renderer covers the ball of UU itself, but there are still two pieces that can be covered better by a normal renderer:
A 2-pixel-wide base plate on the side where a machine is connected.
A single-pixel-wide tube connecting the center of the base plate to the center of the UU ball (0.5,0.5,0.5).
[ ] Include the special renderer's character data in the NBT save/load
[ ] Include the special renderer's character data, as well as the internal tank fill level in the block description packet. Don't forget to mark block for update once in a while as the fill level changes.
[ ] Regenerate the special renderer's character data if it's not available for any reason (e.g. the tank was emptied)
There used to be four issues for this, but Github lets us make these checkbox thingies now: