Patrick, zincs that are eroding is a good thing. That means they are providing protection as they are supposed to erode. It's when corrosion/erosion shows up elsewhere (for example, a pump impeller) that you have a problem. That means that the pump is not protected by the sacrificial anode. As for the macerator pump on your heads, I thought those motors were already bonded. Seems to me I saw a bonding wire on mine, although I'm not on my boat right now.
S/V Celtic Cross