I guess the simplest TM would consist of a motor (air or water cooled) hooked up to a blower (direct or pulley) and a pump by pulley. As the engine runs it drives the blower and pump which creates vacuum and pressurized water. In between the blower and the wand is the waste tank. As the water enters the system it is pressurized at the pump and sent to the wand then recovered and sent to the waste tank.
If there was a heating system on this it would either be fuel fired or HX.
If fuel fired - the water would pass through the boiler before being sent to the wand
If HX - the water would pass through the HX, which is heated from the exhaust or coolant from the engine before being sent to the wand.