After issue #2611 is closed. I looked at the code of DynamicFluidTank.java and tested it, the problem still persist.

This line
https://github.com/aidancbrady/Mekanism/blob/development/src/main/java/mekanism/common/content/tank/DynamicFluidTank.java#L116

should return "prevNeeded" instead of getNeeded() because it will still return 0 thus draining nothing.

Fixed, thanks