I have not seen the one mentioned in the previous threads but I made my own undercarriage setup a couple years ago. Took a 5' pipe and bent it about in the middle about 45 degrees, bought the driveway washdown assy I saw in Dultmeier magazine, put a hose swivel between the wand and the wash down assy, with a trigger gun on the other end. Two prong FB wand holder to hang the gun on the wall. There are 3 nozzles -2502- .
I have a big sign over the bay and have done radio ads with disappointing results. Have done about 30 hours of use in 2 years (9/2011 9/2013) with 15 hours since the first of this year to 9/30/2013.
I apply a corrosion inhibitor through the wand.
From the usage I have observed it does not create more mud in this bay. I have only seen a couple of customers attempt to hold the wand up to the vehicle but is awkward to use in this manor.
On the discharge of my pump I installed a NC solenoid valve on the undercar line and a NO valve on the regular HP line. When the undercar is selected both valves are energized and pressure is diverted to the undercar wand.