Macerator pump should be
very close to the level of the tank discharge fitting. It can be SLIGHTLY higher, but not high enough or far enough away to let the impeller run dry for more than a couple of seconds...the friction heat from running dry "fries" the impeller. Even those couple of seconds creates enough friction heat to gradually degrade the edges of the vanes, which is why it's very good idea to change the impeller every spring as a part of the boat's spring recommissioning. And you'd be smart to keep a spare aboard at all times. If you lay up for winter, there's another good reason to change it every spring--in fact, changing ALL the impellers every spring is a good idea: over the winter, neoprene dries out and becomes hard and brittle...sewage or salt in the housing can "glue" it to the housing, and the first time you turn it on puts a LOT of strain on the vanes--which are dry and brittle. Many a boat owner has tested an impeller pump at spring launch, thought it was fine, only to find it didn't work the first time he actually tried to use it...'cuz the test cracked a vane that finished breaking off the second time. The same thing can happen if a boat sits for a long time, or a pump isn't used very often. The more you use some things, the longer they work without problems.
