Originally Posted by
MudPie
The other variable about o-rings is the material. Some materials are better suited for different chemicals or environmental conditions, but for this applictin, the cheapest and most available rubber will be more than sufficient,
Most hardware store/plumbing are going to be SBR or Buna N (Nitrile) and more than adequate. Auto parts may have a Viton (FKM) for fuel applications, but would be overkill for a pump.