GMC Created a Motorhome Designed to Intentionally Discharge Sewage Through Its Exhaust

The GMC Motorhome from 1973 remains an iconic presence on the roads today. This innovative recreational vehicle (RV) boasts a striking design, features a V8 engine powering the front wheels, and showcases an interior that epitomizes the vibrant style of the 1970s. Interestingly, during this era, attitudes towards what could be released into the environment while driving were quite different, even allowing for the expulsion of sewage through a unique option available for this GMC model.

Among the options for the GMC Motorhome was a system known as Thermasan, aimed at alleviating one of the most unpleasant aspects of RV ownership: managing black water. This term refers to raw sewage that collects in an onboard tank, which must be disposed of at designated dumping stations. The unpleasantness associated with this task led to the creation of the Thermasan system by a thoughtful employee at RV accessory company Thetford Corporation.

The Thermasan, marketed as a “waste destruction system,” was based on a straightforward principle: it would expel black water through heated exhaust to sanitize and dispose of waste. The maintenance manual for the 1973 model details a method utilizing a pump powered by a wiper motor, linking the black water tank to the exhaust just before the muffler. A screen was incorporated to prevent solid waste from clogging the system, which would be a nightmare to repair. Interestingly, Thetford termed the discharge point the “ejection orifice,” a name that is bound to provoke a chuckle.

The Thermasan was managed via a control panel located to the right of the steering column. This panel featured an on-off switch, a pump test switch, and three indicator lights. It would activate once sensors detected that the vehicle was traveling faster than 35 mph and exhaust temperatures were above 900ºF. This mechanism ensured the high temperatures necessary to sanitize the output and aimed to make it odorless. At that speed, the system, which had a maximum flow of five gallons per hour (or one teaspoon per second), would ideally prevent any significant waste accumulation on the streets.

However, the Thermasan was not designed to eliminate all waste; solids would remain behind the screen. It also intentionally did not fully empty the tank to prevent the remaining waste from drying and hardening. The manufacturer estimated that users would need to perform a traditional waste emptying only once or twice a year.

Ultimately, the Thermasan system did not gain widespread acceptance and is absent from today’s RVs. A former employee of Thetford discussed the reasons behind this in a forum dedicated to GMC motorhomes, attributing its failure to the historical context. The year 1973 marked the oil embargo and the establishment of the Environmental Protection Agency, leading to a decline in sales of large, gas-consuming motorhomes and financial struggles for their manufacturers. Furthermore, states began enacting their own emissions regulations, and Thetford could not convince them that Thermasan would not interfere with these standards.

The situation was exacerbated by concerns raised in Thetford’s promotional materials, which suggested that odor molecules would be incinerated. However, the former employee revealed that the waste’s urea and ammonia were not treated, resulting in what he referred to as a “hot diaper smell” while the system was operational. This revelation certainly does not help matters.

In conclusion, it’s fortunate that RV owners did not adopt this waste disposal method widely. While it may have offered convenience, the implications for other drivers on the road could have been quite unpleasant, in addition to the ongoing maintenance challenges it would present. Ultimately, a society where individual convenience takes precedence over collective well-being is not sustainable.

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