A Disturbingly Close Look At The 1970s RV Technology That Cooked Your Poop As You Drove Down The Highway

Fifty years ago, a major RV supplier pitched a way for camper owners to easily empty their rigs’ black tanks. Why deal with the sometimes messy and smelly process of dumping your tank when your motorhome’s or tow vehicle’s engine could do it for you? The Thetford Thermasan Waste Destruction System emptied your tank by taking your poopy water and spraying it into your RV’s exhaust manifold, burning it in your exhaust. This is a real thing that existed, and you can sort of buy something similar today.

Last week we had a chat with Bring A Trailer Co-Founder Randy Nonnenberg on our podcast. In it, Randy, Beau, Jason, and David talked about the coolest vehicles to ever roll across the virtual Bring a Trailer auction floor. One of them was an epic 1972 Ford Condor II motorhome that once belonged to McLaren Engines chairman and CEO of McLaren Racing Zak Brown. The RV itself is pretty cool, or baller, as the kids would say.

But readers had a question about this paragraph in the Bring a Trailer listing:

The kitchen area includes a refrigerator, freezer, pantry, and a kitchenette with a single-basin sink, oven, stovetop, and wood cabinets. The adjacent bathroom is equipped with a Thermasan waste destruction system that was designed to dispose of liquid and organic waste materials through the exhaust system.

You read that right. This vintage RV is equipped with a system that takes the liquids of your black tank and “disposes” of them in your RV’s exhaust stream. But how did it work? And what happened to them?

[Editor’s Note: I’m going to start saying “evacuate my holding tank” whenever I take my bowels for a spin now. – JT]

Alternative Methods Of Dealing With Your Crap

The idea of dealing with human waste in vehicles goes back about as far as the RV itself does. However, back then, somewhat similar to how it is today, dealing with human waste often involved filling up a portable toilet and dumping it later on. It’s hard to say when inventors began to consider burning up waste, but the seeds of the Thermasan system were planted in 1931 and 1948, respectively.

In U.S. Patent US1892132, published in 1932, inventor John L. Berney shows off an atomizing system fitted to an airplane’s exhaust. This system is designed to atomize pesticides in an airplane’s exhaust, leading to the pesticide landing on crops. And in U.S. Patent US2658202A, applied for in 1948 and published in 1953, inventors Abel Wolman and William A Hazlett created a system for a vehicle to dispose of human waste.

In this system, wastes would go straight from a toilet and into a grinding machine or macerating machine. Once the waste is ground into small particles, they would go into a holding tank. The waste would then flow into a heating chamber, where the waste would be disinfected through a heating process. Once the waste particles are heated to 170 degrees and once the vehicle reaches a determined speed, a valve opens, disposing the apparently disinfected waste onto the ground. The inventors note that dumping heated poop particles onto the road might be unsightly, so it’s designed to spread the discharge out.

The Thetford Corporation–a company known for RV plumbing products–would reference these patents, as well as a 1961 patent from Airstream for a toilet that burns waste, when it would patent the Thermasan Waste Destruction System. The Thermasan effectively combined attributes from a number of the aforementioned systems and more into one. In its patent, Thetford reveals that it wasn’t the only company working on a way to burn waste. There was another patent for a a system that burned waste in a drum fitted around an exhaust.

I haven’t been able to pinpoint exactly when the Thermasan system first hit the market. The earliest example that I could find was the 1964 Ford Condor motorhome, which was noted in MotorHome Magazine as having the Thermasan system. Thetford itself was founded just a year before.

How The Thermasan Works

So, how does the Thetford Thermasan Waste Destruction System work? Thankfully, there are brochures and data sheets archived online.

First, you switch on the system. Thermasan will only destroy wastes when the engine is hot enough and when the vehicle is traveling at a high enough speed. When the engine is hot enough and when you’re going at least 30 mph, the system can activate. If conditions are correct, an injection pump will operate that pulls wastes out of the tank. A probe in the tank makes sure that what gets picked up by the pump doesn’t have waste suspension. The pump meters the flow so that not too much liquid is introduced into the exhaust flow. Next, the waste is injected into the exhaust flow at its hottest point, which Thetford says in the brochure should burn the waste up so well that there are no visible discharges from the exhaust or a smell.

How it works in depth is pretty neat, and involves a bunch of parts. A question that you might have is how does this 1960s-era system know when you’re going fast enough, or how the engine is hot enough.

In installation documents, Thetford explains that the system measures speed from a speed sensor installed in-line with your speedometer cable. How that works is that you’d remove the speedometer cable from the transmission, install Thetford’s speed sensor, then install the speedometer cable on top of the sensor. In the installation documents, Thetford warns not to install tighter than finger-tight, warning of the damage that can occur.

A wire then runs from the speed sensor to a plate that contains a vacuum sensor, and then to the control head assembly. When you reach or exceed 30 mph, one condition is met for Thermasan to work.

Next comes what Thetford calls a heat sensor in the brochure, but a vacuum sensor in the installation document. All this sensor is looking for is 16 1/4-inches to 17 inches of vacuum. Thetford expects the vacuum line to be installed on a source originating from the intake manifold. When conditions are met for both vacuum and speed, the system tells you that it’s ready to burn your crap.

There are multiple versions of the Thermasan, and the one you get depends on what kind of equipment that your RV has. There’s a version for RVs that just have a black tank, a version for RVs with a single combined tank, and a version for separate tanks. No matter the version chosen, the person installing the system has to drill into a flat spot on the tank to install the probe. From there, a pump extracts fluids from the tank.

The final part of the system is called the Sanijector. This is supposed to be installed on the hottest part of your exhaust, but after the catalytic converter and before the muffler. For this, you drill into your exhaust pipe, place the Sanijector, and secure it with exhaust clamps.

It seems installation is easy enough for anyone to do. And if you’ve checked the brochure by now, you’ve probably realized that Thetford marketed these for travel trailers, too. How does the system work when your RV doesn’t have an engine? Well, Thermasan systems meant for travel trailers would have a hose bringing the wastes to the exhaust pipe of the tow vehicle to be burned there.

Using The Thermasan

Of course, you’re probably wondering, as I also wonder, how this system works in practice. Sadly, it seems like there aren’t any reviews of how this system works. There are forum posts, but few of the people in them ever actually experienced the system. One person says that the system does such a complete job that you don’t smell anything. Another is a post from nine years ago from someone claiming to be an engineer for the Thermasan. They say that they had to work hard at controlling the system’s injection rate so that their laboratory didn’t smell like a “roasted diaper.”

And in the documentation from Thetford, the company warns that there can be an odor present from the vehicle’s exhaust if the holding tank wasn’t diluted with enough water or a Thetford treatment chemical called Aqua Kem. I shudder thinking about following behind an RV that smells of burning poop.

In addition to that warning, Thetford also says to avoid putting things in the toilet that holds strength in water like facial wipes. Today, I’d imagine that list would also include cleaning wipes and paper towels. The Thermasan system can only burn things that dissolve in water. And amusingly, Thetford tells you not to pour stuff like gasoline into your RV’s black tank.

But if you can live with all of that, Thetford says that your Thermasan Waste Destruction System will turn your RV into a mobile, pollution-free waste destruction plant. And you’ll “join the unhooked generation” as you blow past dumping stations as your engine burns your poop.

This system was marketed for a number of RVs back in those days from Airstreams to the famous GMC Motorhome. It seems that the system was marketed from the mid-1960s to the late-1970s. Then, it appears that the product disappeared from the market. It’s unclear when this happened, and Thetford doesn’t even note the product in its history. I would love to know why these were eventually taken off of the market. I’d also love to know just how many of them were produced.

And if you’ve read all of this and you’re still interested, you can actually buy something like this today. Inventor Namon Nassef made a new interpretation of the Thermasan back in 2011, but it looks Nassef never got the investment to put it to market. You can buy the Incinolet, a toilet made for boats, cabins, basements, trains, and other places where you might not have sewer access. Like the Thermasan, it burns your waste. But instead of using a vehicle exhaust, it does the job on its own.

To answer my questions and more, I reached out to multiple representatives at the Thetford Corporation. After about a week, I haven’t received word back from the representatives. Thus, my research has reached a dead end. If you know anything about this rather interesting system, even if it’s just experience using it, drop me a line at mercedes@theautopian.com.