I have a 50 meter garden hose & a 30 meter (about 90 yards in yank speak) 19mm dia (3/4"), I join them both together and lay them on the cement driveway. After they are joined I run water through them till the water flows freely (no air bubbles), turn the tap off but leave it connected to the hose, and turn the nozzle off also. They get heated by the sun very well about 50'c in 2-3 hours (about as long as it takes to extract). when your ready turn the hose on and away you go, about 90 litres of hot water.
cheers
Mark