Take them apart, and put all bearings, the impeller shaft and impeller into a cup (separate them into individual components, but put them in the same cup) and then add enough distilled malt vinegar into the cup to cover everything. Next, turn the pump upside-down and pour the vinegar into the impeller-well. Now leave to soak for about 2 hours, before rinsing in warm water, and wiping off any remaining residue as you dry it all out after the rinse with a tissue If the pump is something like a Maxijet, the flange will need to go in the cup also