Buildcraft version: 7.99.7

Distiller accept only 0,999 bucket from every full bucket of Heavy Oil, 0,001 left in pipe.

seems to be intended behaviour, the distiller only accepts fluids in multiples it can process without any leftovers. It's not accepting the 1mb because 1mb isn't enought to process

But with other liquids Distiller accept full bucket.
I think this is calculation error.

if it accepts the full bucket with other fluids it isn't a calculation error. Different fluids have different processing ratios, the heavy oil processing is in multiples of 3, the other recipes do have ratios that perfectly devide a full bucket without leftovers

pinging @AlexIIL for if we want to do/change something for this but this currently is intended behaviour

I think leftovers in pipes is bad idea.
Distiller must accept full bucket, but output is subject of discussion.

it's a design choise, the leftover is eighter in the pipe (where you can redirect it to a tank if you want though we're talking very minute amounts) or in the distiller itself where you can't get it out again without placing it again (clogging up the tank so it won't accept any other input fluids until then)

I can probably simplify this by changing the amount of heavy oil used in processing from 3 to 4, which divides evenly. (All of the other numbers divide evenly, so it's not really an issue for them).

I think it's not matter in mass produce.