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DIY RV Macerator Pump

Author: |
Aug
24
2009
 Posted in Favorites, Projects 28 Comments

When you own an RV one of the things you have to deal with is dumping the waste tanks at the end of your stay in a campground.  This is generally not a big deal, you pull up to the dump station, usually located along the driveway on your way out, hook up your waste hose and dump your tanks by opening the 3" slide valve.

But what do you do if you go camping somewhere other than a campground?  Well, south of the Mason-Dixon line you will find  numerous facilities where you can dump for free or for a small fee, but such services seem to be a whole lot rarer up North.  In my case we often take the RV up to visit my sister and her family in Maine and park in their driveway. There's really no conveinient place to dump when we return.

So I decided to see if I could cobble something up to make this task easier.

The solution to dumping your tanks without having to carry a 100' 3" diameter hose is to use a macerating pump so that you can pump your tanks out through a garden house and into a city sewer or private septic system.  There are commercial pumps that you can buy for this but I had this old Insinkerator Dispos-all kicking around . . .

Step one was repairing the garbage disposer.  This turned out to be pretty easy.  Leakage around the seal had caused the top bushing to seize and spin in it's clip causing the rotor to bind against the stator.  I freed everything up, re-secured the bushing, and lubed it with axle grease to help keep it free.  My guess is that I would face the same problem if I re-installed the dispos-all in the sink, but it should last for many years with the light "duty" it will get as a macerator pump. 

Once I got it working I found, to my delight, that the top of the disposer – once all of the gaskets and flanges were removed – was exactly 3" in diameter!

I drilled and tapped (4) 5/16" bolts into the top and had a perfect seal!

Next I drilled a 7/8" hole in a piece of 1/8" brass and soldering in a brass garden hose fitting.  This bolted in place of the original drain flange.

The completed black water macerator pump! The dishwasher connection was plugged with a #2 rubber stopper inserted from the inside.

I made a waste hose with two 3" female fittings and hooked everything up.

I pried up the edge of our septic tank lid and tucked the hose in.  Next I opened the waste valve and  turned on the power.  It worked like a charm!

It drained the half full 100 gallon tank in about 10 minutes and handled all of the solids without the slightest complaint.  I briefly held the hose as high in the air as I could and the pump had sufficient head to lift the water 7' while maintaining plenty of flow.

Once the tank emptied the hose could easily be reposition to let the last bits dribble out.

I'm quite pleased with this quick little hack!

About Author

Jake von Slatt

Comments
  1. Posted by Gershey

    Thanks so much for your post. Great work!! I built mine last night and it worked like a champ. It pumped the waste about 100′ to my septic system. I didn’t have any brass plate to use for a hose adapter so I used a marvel adapter on the included drain pipe with a 1-1/2” sch 40 pipe connected to a 3/4″ bushing and a sch 40 to hose adapter. I love it.

    • Posted by Jake von Slatt

      Yay! I love comments like this!

  2. Posted by Dave

    Great craftmanship on your unit ,could you recomend a minimum horse power rating on the
    Disposal unit.

    Thanks dave J

    • Posted by Jake von Slatt

      The unit I used was on the cheapest economy dispos-alls on the market. I’m sure any unit will work well.

  3. Posted by Luke

    A quick qyestion? Can it work laying down or does it need to stand up!???

    • Posted by Jake von Slatt

      I think it will work fine on it’s side, but I have not tried it. Eventually I plan to build the disposal into my bus and when I do I plan to lay it on it’s side.

    • Posted by casey king

      Waste needs to be “dropped” into the disposal onto the rotating grinder plate where it is spun to the teeth at the outer rim then out the port. Turning unit on its side would probably cause solids to accumulate and cause clogs.

      I am working on a compact, all in one portable wet bath (footprint is 2’6″ x 4′). I am installing a setup like this with hard piping behind a wall-mount toilet. I would love to mount disposal on its side, i just don’t think it would hold up long term.

      Also using dishwasher port to drain sink (above toilet) and shower (has it’s own dishwasher pump and check-valve to pump up). Anyway, my original plan was to install a Whirlpool washing machine pump on bottom of disposal using the 1/4″ hex on bottom of disposals motor shaft. But after an initial bench test with disposal, i may eliminate the washer pump and rely on the disposal. Before i get too far into it, was searching for info on pumping ability of one of these kind of disposals. I need to discharge out of a 1″ schedule 40 PVC or 3/4″ hose at least 120′ horizontally. Any thoughts or ideas would be appreciated!

  4. Posted by Steve

    thanks Jake, for sharing such a great invention with everyone. I plan to put it to good use multiple times. To bad some people insult you because they don’t understand the whole concept and the utility of what you have come up with.

  5. Posted by Jon

    what about those sanitary wipes women like to use? my wife uses them sometimes and I am afraid it might jamb the gears up. your thoughts?

    • Posted by Jake von Slatt

      I suspect they would. But in general those things cause headaches for treatment plant operators and are absolutely not for septic systems . We stuff them is a zip lock baggie and toss them in the trash.

  6. Posted by Tom Grant Sr.

    I loved your idea, so my brother and I took it a step further.
    We used an elbow connector he had for his waste line, ’cause it fit perfectly in the sink flange of the disposal. We also used the dishwasher inlet for fresh water input to flush the whole rig when the tank is empty. We clamped a garden hose shut off valve on the inlet with a short length of 3/4″ vinyl tubing and then screwed on a garden hose to flush. We went with a 1″ x 100′ roll of black plastic water line for the output to the septic tank (actually took another 25′ to reach.) It fit perfectly inside the drain port with just a couple wraps of electrical tape and hose clamp. We put a back flow valve about a foot from the output of the disposal to prevent back flow due to the 4′ rise to the septic tank. We cut a 5 gal bucket to fit it all in and drilled holes in the bottom, so it could drain if needed. We also drove a post in the ground next to the bucket to hang the plug up off the ground and just plug it in to an extension cord to operate. It drains the tanks quite fast and has plenty of push to give a full pipe of output at 125′ and 4′ foot rise.
    Thanks for the idea!

    • Posted by Jake von Slatt

      That’s awesome! Thanks so much for the update!

    • Posted by casey king

      Awesome! Thanks for sharing!

  7. Posted by tom

    great I have a old working one out in the yard im going to make mine now thanks

  8. Posted by Craig

    Very cool idea.

  9. Posted by David

    Fortunately this does a GREAT job at chopping up the solids and unlike a real macerator pump you don’t have to worry about running it dry. The overlooked part is that this is NOT a pump. A garbage disposal only chops solids up and gravity does the job of moving the solids and water along to the sewer. To prove this fact, take a look at the video showing a cutaway of a garbage disposal on ThisOldHouse. The link to the video is at

    http://www.thisoldhouse.com/toh/video/0,,20210077,00.html

    So if you want to use this design to pump RV waste then you have the wrong solution – it does NOT pump. Now you could figure out how to add a effluent pump downstream of this garbage disposal. I’m still on the fence on buying a real macerator pump for my RV for home dumps because of the sensitivity these pumps have with running them dry – doing so to many times damages Flexible impeller – see an example of this at:

    https://en.wikipedia.org/wiki/Flexible_impeller

    • Posted by Jake von Slatt

      Um, I’ve been using it for several years now and it totally will lift liquids at least 6 feet. It may not be *designed* as a centrifugal pump but it certainly works as one.

      • Posted by tom

        thank you for lettin me know it works

  10. Posted by Addison

    This is what I have been looking for, thank you for posting. I am wondering how it’s bee working? How many gallons you’ve pumped through it? Also of you have made any improvements.

    Thanks
    A

    • Posted by Jake von Slatt

      I’ve made no modifications and it’s been working perfectly. Not sure how many gallons have passed through it, probably thousands?

  11. Posted by Chris

    I’m not sure how I got here. I started looking for steampunk leather masks, and somehow ended up reading an article about a poop chewing machine. It’s gorgeous! That is really nice work and makes me regret that I threw away a perfectly good disposal when I could have bought an RV and made a poop chewing machine for it. You have a fascinating website and I’m looking forward to wasting my entire day tomorrow going through it.

  12. Posted by Duncan Millar

    You could hookup fresh water hose to dishwasher discharge to rinse system.
    Just use back flow preventer on fresh water hose

  13. Posted by Phil

    Well put, Jake.

    • Posted by Phil

      Obviously this was my first post. Apologies for the placement.

      • Posted by Jake von Slatt

        No worries! Thx!

  14. Posted by Louis

    Or….you cold buy a $50 pump….instead of all that crap…

    • Posted by Jake von Slatt

      This is clearly not the website for you.

      • Posted by eralov

        try finding a decent pump for $50. great write up and idea.