The manual water pump should continue pumping until I stop or until the tank is full.
It's really annoying to have to press E and repeat until it's full.

Or instead of backing completely out of the animation the character 'waits' until you hit E again or left click and keeps pumping

The animation will be fixed to loop more easily, but we won't ever make it that pumping it once fills the whole tank. It's supposed to be inconvenient.