You got it Russ, the engine will keep heating water, and if this gets excessive it can cause damage to parts of the system.
On the Prowler you set the temperature you want to work at. When the temp exceeds this a valve opens and the hot water "dumps" to waste, thus introducing cold water into the system.
On most machines with tanks, this "waste" water, which is clean, dumps to the waste tank. On the Prowler it dumps thro the waste pipe to atmosphere.
The water gets excesively hot usually when you put the wand down to move furniture, or pre spray. Provided with the Prowler, apart from 100 ft suction, 100' solution, and 50' discharge hose, you get a wand (and its a good wand) with a manually operated by-pass valve. When you stop wanding for a time, as described above, just crack this ope and there is a continuous flow through the machine which should prevent dumping to a great extent.
What I did with the prowler waste hose was place it in the border or shrubery. I was thinking of getting one of the smaller wheelie bins, placing the waste hose in it, via 2" connector, to collect dirty water, and have a standard garden hose at the bottom running off to a dirty water drain ie external kitchen drain. There is a large amount of force from the waste pipe of the Prowler and there would have to be a way of keeping the lid of the bin shut down or water would be flying everywhere.
May be someone done something similar?
I was more then happy not having a waste water tank with the Prowler, not a nice job cleaning out a dirty smelly waste tank - had to do it with the Chemspec Avenger I had.
The more you spend on a TM the more sophisticated it gets. This has its plus points, but also more stuff to go wrong as well. The Prowler won my vote because of the simplicity it had.