reverse

I can't single out a dosing pump that has a reverse functionality and was wondering if anyone could list a few. Size doesn't really matter as long as it can be automated to pull fluid back into the reservoir after pushing it into the aquarium. The idea is that you can auto dose refrigerated...

It does not happen all of the time, but every once in a while my WAV runs in reverse. It makes a buzzing sound when it does so. Here is a video and a screenshot of my settings. Any ideas why and how to stop it?