Bonk, bonk,bonk,bonk - in the middle of the night. Everyone is awake. Five seconds remission then - bonk,bonk,bonk again and so it goes on. I serviced my Jabsco toilet pump recently and cut two washers out of 1/8" thick foam approximately 3/4" diameter each with a 5/16" hole. One fitted below the sliding seal on the pump stem and the other above. Now, if there is any bonking going on in the night it doesn't wake us!