Dave,
water is passed down the solution hose to the wand,if you use a "heat and run"the solution pipe is connected to the heat and run via quick connectors so the water is now travelling through the heat and run and then carries on down the next length of solution hose to the wand.
As it passes through the heat and run it is heated.
You can use a short length from the porty to the heat and run or if working some distance from the porty you would be better connecting it nearer the wand,
Please feel free to ask/call if you want any more info
Paul