The RV Macerator Project (1/28/04)

One of my pet peeves is finding a dump station en-route after returning home from a trip.  Usually our last camp site is 6 to 8 hours from home, and even if we dump at the campground, the “facilities” are normally used underway, so we usually always return with something in the tanks.  The other alternative is to wait until the following weekend and take it somewhere and have it done, but the cost of gas, plus the distance to the nearest dump, plus the dump charge when I get there makes it about a $10 - $12 project

At first I was going to add a cleanout to my home sewer line next to the house to a dump station, but unfortunately it is a slight uphill grade from where the Motorhome is parked to the sewer line, so the normal dump method won’t work for us.

After reading about several people that use them, the macerator seemed like our best solution.  I can see where it might have several advantages:  One is that it doesn’t take a lot of room to store it and 50 feet of hose, two is that it will pump uphill, so even a nearby toilet, or sewage vent pipe (if you want to crawl up on the roof) can serve as a dump station, and three that I’m hoping that it will be generally “less messy” and easier cleanup.

I had looked at two “store-bought” versions, one which had a pump inlet the size of the standard “slinky” sewer hose, and another that allowed you to fasten the pump directly to the RV’s sewer discharge pipe.  Neither one of these appealed to me either because of the potential for mess using the large inlet hose, or the risk of the pumps weight breaking off the locking ears on the discharge pipe.

The way this one is set up allows the pump to sit on the ground alongside the RV with no strain on the outlet and it breaks down into two pieces plus discharge hose.  I plan on using one of the flat roll-up hoses like you see advertised on TV.

Here is pretty much everything except for the flat, roll-up discharge (garden) hose (as seen on TV). Probably the most time consuming part was trying to come up with a clutter-free way to reduce the large RV sewer discharge fitting down to 1-1/2” diameter to fit the pump inlet, in such a way that the plumbing could easily be removed for storage in my small “basement” locker, and then chase down the parts. The right end of the radiator hose is a pretty snug fit to the pump without the clamp, but I’m “storing” the second clamp on the hose just in case the fit gets sloppy and leaks air. Since the pump is fairly current hungry (20 amps), I  used #8 stranded wire to make the 20 foot run to the cabin batteries.  The black fuse block shown may be replaced by a single 50 amp “maxi-fuse” and holder.

The pump itself is a Jabsco “Self-Priming, Waste/Livewell pump”, and will “chomp” and pump 12 Gallons per minute, so emptying my tanks should take just under 6 minutes.  The current draw is rated at 20 amps.  The inlet is a hose barb type fitting, and in 1-1/2” in diameter.  The discharge is also a hose barb type, and is 1” in diameter. When I made the box, I chose to mount the pump upside down so that the discharge was at the bottom of the pump housing, and pointed to the outside instead of underneath the RV. The handle and switch are self-explanatory, and the little rubber feet came from the bottom of my surround sound sub-woofer which wouldn’t clear the entertainment center shelf without removing them.  Probably the most difficult part to locate was the discharge fitting (with the smaller red cap).  It is brass, and has garden hose threads on the right-hand end, and pipe threads on the other.  I used 6 wraps of Teflon pipe tape to make a better seal with the pipe threads.

This is a closeup of the "pieces parts" that I kluged together for the inlet side which is pretty much self explanatory. One change I did make was to replace the Wal-Mart adapter, with a little bit better made clear plastic adaptor.  The first time I tried it I found out that the adaptor wouldn't fully seal, so I'm glad that I was testing with "grey" water. Like I mentioned above, the second clamp on the radiator hose is there for "storage" for the right-hand end until the hose stretches and will no longer seal on it's own, then I won't have to hunt one down.  For now it fits snugly enough that it's not needed..

These are 50 amp DC connectors, (available from NAPA auto), and are similar to the large electric fork truck connectors.  I’ll have a short pigtail with one of these connectors in my basement locker, and another 36” pigtail and the second connector attached to the pump.

This is a homemade terminal block.  Since the #8 wire is pretty stiff, I needed these for a strain relief to allow me to connect to the pump and battery with short lengths of more flexible (expensive) cable The terminal bolts were recessed on the back side using a “forstner” bit, and then is backed with some clear Lexan for insulation in case the bolts work loose.  (one of these will be mounted on the vehicle frame rail, and the other on the inside of the galvanized storage locker)