Braided steel washer hoses, that can't split open like rubber ones. Metal dryer-vent pipe sealed with foil tape, rather than a plastic flex hose. A washer box that's recessed in the wall so that water valves are easily accessible and hoses don't loosen or get damaged by getting squished behind the machine.
Customer review on non-marking pressure washer hose, "These are great pressure washer hoses. We have purchased many of them for all of our pressure washer setups and so far none of them have failed us. We put them through some pretty tough use. Though we try to take care of them around sharp metal edges sometimes there is no avoiding their being pulled across a roof edge, but they have held up." -ArkyDawg from Mountain Home, Arkansas