By adding a macerator pump system, dumping your motorhome’s holding tanks can become an almost pleasant experience.
By Mona Vanek, F337819
Emptying motorhome holding tanks can be worse than annoying. This fact became even more apparent to my husband, Art, and I last fall during our maiden trip in our first type B motorhome, a 2002 Roadtrek 190 Personal, after downsizing from a 32-foot type A coach. Although we are veteran motorhome travelers (150,000-plus miles), after two weeks of exploring the Oregon coast, we decided to investigate ways to improve the tank dumping process in this smaller coach.
Before we embarked on 7,600 miles of winter travels, Art converted the Roadtrek’s sewage disposal system by installing a macerator pump that grinds up sewage and ejects it. Now we can drive up to sanitary dumping stations, open a compartment, pull a small retractable hose to the sewage receptacle and attach it. Then we open the valves, flip a switch, and, faster than you can sing America the Beautiful, that once odorous and unsanitary chore is accomplished almost effortlessly “” and practically white-gloved. Our do-it-yourself conversion didn’t require a large compartment, and it cost less than $500.
Many motorhomes, regardless of make, model, or vintage, can be similarly equipped, although some methods or installation steps may differ slightly depending upon the application. If you’re a handy backyard mechanic, this article will help you make over your motorhome. If you don’t know a screwdriver from a pancake turner, have the job done by a professional.
Art chose the model 5800 RV Sani-Con system. The unit measures 6 inches by 6 inches by 4 inches, plus the inlet apparatus. Art easily modified it to fit into a 10-inch-wide-by-17-inch-long compartment that he constructed. The compartment fits into the narrow space formerly used by the ABS casing that contained the slinky hose (on larger coaches, this compartment may or may not be necessary).
The goal is to connect a solid ABS pipe system from the tanks to a macerator pump housed in a compartment that opens flush with the motorhome exterior, thereby eliminating the “stinky slinky.” You still have the “slinky” (now a sewer hose that’s smaller and more sanitary) but not the “stinky.”
Determine your sewage system design and the materials needed. Look at the underside of your coach. Where are the holding tanks and the tank-valve rods? If the holding tanks are under the curb side of the coach, chances are the tank’s gate valves empty into an ABS T-pipe connected to a 3-inch ABS pipe that extends to the street side, where the sewer hose (slinky) attaches. However, these components may be configured in the reverse order, or in some other arrangement. Depending on your motorhome sewage discharge system, you’ll need an ABS outlet pipe and adapters. You’ll also need some 3/4-inch PVC pipe, elbows, and clamps and cement for ABS and PVC pipe.
Locate sufficient undercarriage space to accommodate a metal compartment approximately 10 inches wide by 17 inches long. The ABS sewer pipe will couple to the pump inside this compartment. The sewer pipe must not be higher than the bottom of the holding tanks and should slope at least slightly downward, not upward. The area can extend toward the center of the chassis or be lengthwise, and needs a door to the outside of the coach to allow access to the retractable discharge hose and the pump’s switch.
If you’ll be utilizing an existing sewage compartment door, remove its lock-latch. Remove your holding tank rods and save them for reinstallation later.
If necessary, to create space for a compartment to house the RV Sani-Con system, shorten the 3-inch ABS pipe to which the slinky is attached. You’ll require an adapter and collar to connect the 3-inch ABS pipe to the pump inlet.
Creating a compartment
Using 1-inch-by-1-inch-by-1/8-inch angle iron, make two L-shaped frames approximately 16¾ inches by 6 inches (or to fit the available space). Paint the frames to prevent rusting. For mounting the completed framing, drill two holes in the shorter ends of the frames and drill matching holes in the coach’s frame. Gussets aren’t necessary in a small compartment.
To take measurements for your compartment, temporarily clamp the L-shaped frames to the chassis. The make and model of your motorhome will determine the width of your compartment, but it must be at least 9¾ inches wide by 16¾ inches long. (Keep in mind that the measurements and instructions are for a modified model 5800 RV Sani-Con system.) Don’t worry if the chassis frame restricts the height where the pumping unit sits near the door to little more than the pump’s size, because behind the frame the upper space (which becomes the rear of the compartment) isn’t restricted.
After you have your measurements, remove the compartment frames from the motorhome and cut 1/16-inch sheet aluminum to attach to the angle-iron frame for the sides and bottom of the compartment. Attach them with sheet-metal screws so they can be removed during the installation steps. Make sure that your compartment will not block undercarriage attachments, such as water tank drains, etc.
Drill small holes near the lower corners for the tank valve rods. If you do not have sufficient space for both tank valve rods, relocate one or both.
Modifying the unit to fit
To position the 5800 RV Sani-Con system, temporarily assemble the compartment. The 6-inch-by-6-inch-by-4-inch pump’s inlet components (as shipped from the factory in Lexington, Kentucky) can be downsized to fit your compartment. Gray water connections to the pump’s inlet and outlet are made up of:
a) A small diameter clear plastic tube attached to the white discharge adapter;
b) A 3/4-inch clear plastic hose attached to the side of an ABS inlet adapter.
Whether you position the unit upright or lying down, make the following minor reductions in the discharge pipe assemblage. When placed flat, both the clear plastic hose and the clear plastic tube will face the side. Two additional 3/4-inch elbows; a 1-inch to 1½-inch length of ¾-inch PVC pipe; and a spring are needed to replace these gray water connections and to replace the 3/4-inch PVC discharge fittings with compact, space-saving fittings.
1. Turn the ABS fitting that attaches the clear gray water tube toward the side of the compartment.
2. Remove the 3/4-inch PVC elbow.
3. Remove the black fitting and save it.
4. Remove the 3/4-inch PVC pipe above the clear hose on the side of the ABS sewage inlet adapter.
5. Drill a hole in another 3/4-inch PVC elbow on the side facing the pump-inlet adapter. Cement the black fitting (taken from the elbow) into the hole. One end of this elbow forms a corner of the discharge outlet.
6. Cut a 1-inch to 1½-inch length of 3/4-inch PVC pipe (long enough to connect another 3/4-inch PVC elbow to the lower end of the discharge corner elbow) and align this end of the elbow with the 3/4-inch clear hose on the side of the ABS sewage inlet pipe.
7. The 3/4-inch clear hose attached to the ABS inlet adapter on the side of the pump couples with the discharge PVC elbow. Slide the hose onto the elbow and clamp both ends of the hose.
8. The clear gray-water tubing connects between the PVC inlet adapter and the PVC discharge elbow. Couple the tubing between the side-outlet on the PVC inlet adapter and the PVC discharge elbow. Shorten the tubing enough to reconnect it to the black fittings on the upper PVC elbow and on the PVC inlet adapter. To prevent the tube from collapsing, slide a spring of the same diameter inside the tubing before clamping the ends of the tubing.
9. Cement a length of 3/4-inch PVC pipe (approximately 7 inches to 8 inches long) to extend to the opposite side of the unit.
10. Cement another 3/4-inch PVC elbow onto it, directing it to the outside of the unit to attach the black flexible discharge hose alongside the pump.
11. Bolt the modified pumping unit assembly into the compartment. If it’s necessary to elevate the assembled unit to align the (white) discharge pipe with the 3-inch ABS adapter coupling, insert brass nuts under each corner of the pump unit.
Completing the sewage discharge system
You’ll be able to take accurate measurements to make the ABS pipe connections after your compartment is built and bolted (temporarily) to the frame of the RV. Configure your connection between the ABS sewage pipe and the pump unit inside the compartment using additional pipe, elbows, and adapters as needed. Make sure the collar on the ABS adapter extends into the pump compartment sufficiently to support the pipe.
Cut a short (approximately 4 inches) piece from the heavy-duty flexible pipe provided with the RV Sani-Con system to join the sewer pipe adapter to the ABS inlet adapter on the pump unit. Slide it onto the PVC pump inlet and slip two loosened clamps over it.
Don’t attach the compartment’s side panel before you’ve completed the process of bolting the compartment holding the pump to the chassis and finished the ABS pipe-to-pump connections. While you are raising and attaching the compartment to the motorhome chassis, the 3-inch ABS pipe inserts into the ABS collar through the hole in the compartment. Connect the sewer pipe to the ABS inlet adapter with the flexible black pipe. The flexible pipe collapses to about 2 inches. Bolt the compartment onto the chassis. (Loctite sealant on the bolts is recommended.) Tighten the clamps. Attach the remaining side of the compartment. Reinstall the compartment lock.
Relocating the tank valve rods
Holding tank valve rods may need to be reshaped and extended to position them close to the outside of the motorhome. Insert the rods into the predrilled holes. If you’ve relocated a rod, fortify the new hole with a grommet and make a bracket to suspend the rod. Make sure the rods don’t interfere with the compartment lock. Reinstall the handles on the rods. After attaching the rods to the holding tanks, use Loctite sealant at the tank ends.
Slide the black flexible discharge hose onto the forward side of the pump discharge PVC pipe. Secure with a clamp. Use PVC pipe and fittings to create a capped nozzle that is smaller than the one supplied, and insert it into the discharge end of the flexible discharge hose. It will store easily with the coiled flexible hose inside the compartment. When necessary, it can be quick-changed with the retractable nozzle provided.
Wire the macerator pump to the motorhome chassis battery with an in-line fuse. Drill a hole in the motorhome compartment that houses the electrical connections. Insert the red wire. After soldering the connections, feed the wire to the pump and connect. Ground the unit by connecting the black wire to the motorhome chassis. Caulk the opening after the wires are in place.
You’ll now travel confidently, knowing that with the flip of a switch you can be singing America the Beautiful while your tanks are being pumped, emptying them without polluting the environment.
Since our purchase in October 2003, the RV Sani-Con system’s model number has changed to model 2104. A newer model 5800 is available, but more expensive.
RV Sani-Con System
1233 Wyndham Forest Circle
Lexington, KY 40514
Learn about macerator pumps and sewage disposal