There are, possibly, two components to the vibration:
1) The vibration of the membrane pump;
2) The clatter from the water pipes.
Here is what I did on my Bav47 cruiser:
1) I attached two lengths of about 3 cm diameter and 15 cm in length clear-braided garden hose across the feet of the pump and screwed the hose pieces to the toilet wall wooden plate. I saw this method used somewhere and it is a quick and cheap vibration dampener (see attached image of my present setup);
2) When the plumbing is semi-rigid, eg 15 mm push-fit tube like on my Bav47, then Jabsco officially recommends for the first 10-15 cm (a figure I invented) connections from the pump to be of a flexible water hose. This reduces vibration transmitting into the plumbing;
3) When the plumbing is semi-rigid, as above, then add cheap hardware store pipe insulation foam around the plumbing, especially near the pump. A lot of energy is carried in the plumbing by the oscillating water. The oscillation is brought about by the membranes in the pump and this can make the plumbing clatter against the wall of the boat.