It sounds like its dumping a lot?
More than mine anyway.
A lot of truckmounts dump water into the waste tank, its how they control the temperature of the water. When it gets to the temp that you have set the machine at it dumps the water, cooling it down.
Have you got the temp set on max? If its set on a low temp it will dump a lot more, even though the temp is adjustable it really should be left on max.
I have modified my machine so that I can either have the water dumping into the clean water OR the waste water tank.
I have cut the hose that dumps the water back into the waste tank and fitted brass quick connectors onto each end. I have then put another hose, fitted with another brass quick connector , back into the FRESH water tank.
So I can now decide wether the water dumps into the clean or waste tank.
The reason that the water is supposed to go back into the waste tank is because hot water is not good for your water pump, and if it is dumping hot water back into the clean water tank all of the time it will eventually heat that water up.
So I start the day with the water going back into the clean tank, but if the level gets to low I divert it back into the waste tank, so the pump doesnt overheat.
Woodbridge will do this for you, its a simple enough job.
But it makes a big difference to the amount of water that is used.
You do need to use your common sense though, and not let the water level get to low.
regards
Chris