Three different pumps got a chance to be on this marvelous project, but only one got to prove worthy.
Or something like that.

The criteria used for this part were that it had to be embedded inside the lid. All three move enough water for all practical purposes, but not all could lift liquid if the feeding tube had air inside.

My favorite was one labeled food grade on Ali. It is potted with epoxy and looks pretty solid. But this one has to be inside the water or just a few centimeters from the water level to work:

This one looks already a bit shady and needs to be submerged to work, so not really a practical solution even though it was really cheap (1€).

And the last one is clunky and sounds like a tractor, but it works. At 5V it needs around 300mA, and there still flows enough water to empty the entire 2,5L in a very short time. For now, this might do:

Moving forward there is room for improvement here. Maybe a peristaltic pump works well enough, maybe a 3D printed one?