Replacing a Macerator Pump

Copyright 1997-1998 by John and Eleanor Coulthard
Permission to copy for non-commercial purposes is granted provided the source is acknowledged

This is the only macerator pump I have ever changed. You are not hearing from someone with a lot of experience. I did this at Beaufort Docks in Beaufort, NC. They let me sit at the pump out slot for hours. When I finished I just moved over one slip and spent the night. Beaufort Marine, about a block away, supplied the parts.

First the layout of my holding tank, which may be different from yours. Our tank has the input to the tank at the top, on the port side. The output from the head goes to a "Y" valve which routes the effluent to the tank or directly overboard through a separate though hull valve. On the bottom there are two outlets. The one in the middle goes to the pump out fitting on the deck. The other, on the bottom inside, goes to the macerator pump. On our boat this is routed via a very short hose to a right angle (from horizontal to vertical) elbow which the macerator pump is screwed directly into. The outlet from the macerator pump goes to yet another through hull valve.

The problem is that pumping out the holding tank does not reduce the level of the effluent to the point where it will not spill out the macerator pump outlet when you unscrew the pump.

Here is my recipe. I did not follow it exactly. Initially I intended to extract the old macerator pump, replace the impeller (which was the prime suspect) and put it back in service again. Bad idea! Life is too short! Loosen your pocket book and before you start have a brand new macerator pump (or rebuilt one) ready to go. When I discovered that my pump problems were not as simple as an impeller replacement, there was a delay while I rushed to the marine store to purchase a new pump. Without getting into details, the rebuild kit would not have solved my problems. This is not the sort of problem you want to solve on the fly while the effluent seeps into your bilge!


New or rebuilt replacement macerator pump - ready to go.


Pump out your tank. Fill it from a fresh water hose. Pump it again. Fill it. Pump it again. By this time the attendant is getting ready to bill you for a second pumpout. Probably not worth it. That little pipe leading to your macerator pump will not get flushed out no matter how hard you try.

Relax with your favorite drink - you deserve it!

In my case there was about an hour's time while I tried to repair the old pump, then went to the marine store to purchase a new one. I plugged the tank outlet with a through hull wooden plug in the meantime. It seeped effluent. Not satisfactory! Even so there was no smell after I finished cleaning up. I think none, or only a trace, made it into the bilge. I did not clean the bilge and my wife had no complaint about a smell. If you really want to take time to repair the old pump it would be best to purchase a properly sized threaded plug for the outlet. In my case the Marine store had no such fitting.

This is messy job. If I ever do it again I will put in a new pump, not my old one rebuilt. As I said, life is too short to spend on tasks like this.

Go to The Galiander Journey Introduction

Revised: November 14, 1998