Home-Brew Macerator Pump

I’m taking a little break from the lithium battery project today.  Usually I don’t stray from hookups long enough to worry about emptying my waste tanks–it helps that I can handle 75 gallons down the toilet, and another 150 gallons of grey water–but for the first time in 10 years, I needed to empty my tanks and didn’t want to move the motorhome.

Where I’m parked, I’m about 150 feet away from a septic access.  I could get close moving the RV, but the tank outlet would be a little bit below the septic access.  So moving the RV doesn’t buy much, and the nearest RV park or dump station is about 20 miles away.

I’ve seen others with 12V macerator pumps and coils of hose, but was never impressed by them–especially considering the cost.  But if I wanted to empty my tanks without a drive, I’d need to pump.  I knew a garbage disposal could pump, and could grind up digested food just as well as undigested food, so I thought I’d give it a try.  A little searching showed that I wasn’t the first with the idea though, which just accelerated the project.

Note that I wanted to end up with bayonet fittings on the disposal, but where I’m at there isn’t one for sale within 30 miles.  Everything except the discharge hose was purchased at Lowe’s.

Here’s what’s needed:

Setting it up is pretty simple.

  1. Pull the sink mounting stuff off of the top of the disposal and push the cleanout adapter on.  While I haven’t done it yet, it’ll be held in place permanently with PVC cement.
  2. Connect power cord to the leads on the bottom of the disposal with wire nuts
  3. Install tailpiece, bracket, and gasket to disposal outlet.
  4. Install coupling on the end of the tailpiece
  5. Connect discharge and sewer hoses.
  6. Start disposal, open grey water valve momentarily, and check for leaks.
  7. Empty black tank and rinse with grey.

In my case, I was pumping through 150′ of hose, with a few feet of elevation gain.  By the time I had walked the length of hose and checked for leaks, the black tank–which had over a month’s worth of stuff in it–was empty.  Rinsing with grey water, the inside of the discharge hoses looked cleaner than a 3″ sewer hose ever does, and laid flat as soon as the water drained out.

I expect to make a few tweaks still to make things even easier.  First, I’ll set it up to directly hook up to a short flexible sewer hose, and mount the disposal in the wet bay.  I’ll also add a shutoff valve on the end of the discharge hose, so that when I’m pumping uphill it’s easy to disconnect without draining it at the RV end of things.  And I might also connect it to the tank level monitor I’ve been working on, just so that I can push a button to start pumping and walk away, knowing the disposal will shut off when the tank is empty.

Quick update:  It’s almost over, but I just saw that Amazon has a more powerful (1 hp instead of 1/3 hp) disposal on sale for the same price I paid.  It’s physically a little bigger, but has over 4,000 largely very positive reviews: Waste King L-8000 Legend Series 1.0-Horsepower Continuous-Feed Garbage Disposal, $87.97

4 Thoughts

  1. How is your home made macerator still working for you? Did you ever replace it with the larger size disposal? If you did was it worth the size difference? It didn’t sound like the 1/3 HP really had any issues. Thanks for great write-up, you convinced me to replace my store bought macerator that is having issues.

    1. It’s still going strong! The 1/3-hp motor doesn’t have any trouble–I now only carry a short length of 3″ hose, just enough to go from the RV’s outlet to the disposal. Even in campgrounds with short reaches to the sewer connection, I’m using the disposal and discharge hose. The only thing still on my to-do list for this project is to order a 10-15ft discharge hose for shorter runs.

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