Yes it can move both ways. And if you deliver at the bottom of the tank, you maybe dont need the dripper, if your hose is thin enough, do that you can dose small amounts correctly.

I personally like steppers, it is very easy to control their position/speed and make accurate pump dosing. And you can easily find hardware/software to get anybody going with them. A RC servo driven pump could also be a nice solution.

Just the pumphead, with motor and control and a thin hose to reach between the 2 tanks. Then you can raise and lower the liquid level.

My 3D printer is not up and running yet, when it is, I will try to make this thing. I need it for my work anyway