Need help please

[HungColt95]

So I bought a pump and it comes with 3 sealing rubber flaps; small, medium and large. I was wondering what is the point in the different sizes and also why do I always get a huge donut when I pump?

 

[engineer805]

Sealing gaskets: choose the most comfortable one that can maintain a good seal (a little lube in the area usually improves sealing). Donuts are caused by vacuum too high and/or session too long.