To get back on track: I don't have wash bay but have cobbled together under chassis spray out of pvc with drilled holes. use for salt. Lot of salted roads this time of year. No pics though.
I built basically the same thing: A chassis washer made from PVC pipe, plastic nozzles, and a quick-disconnect garden hose fitting.
I'm considering having my Ford undercoated with a lanolin- or wax-based coating, and I want to rinse off road salt without damaging the undercoating. The automatic car washes around here have undercarriage washers, but I often wonder if they might be a bit too powerful for a soft undercoating, and besides, driving the truck home from the car wash could pick up more road salt again.
I already had an undercarriage washer attachment for my pressure washer, but it's so powerful that I think it would remove soft undercoating quite quickly. It's also a hassle to set up the gas-powered pressure washer every time I want to rinse off the chassis.
My solution was to make a simple washer that connects to my garden hose to gently rinse off the salt, hopefully without taking any of the undercoating with it.
I can use the washer on any above-freezing day in the winter, and the slope of the driveway drains the water off into the woods. A while ago, I fabbed up a hose setup that lets me keep the garden hose permanently connected to a valve in the basement. I just pull the garden hose out of the basement through a fairlead that I installed (see photo below), and then retract it back into the basement when I'm done. The valve handle is outside, but the hose remains connected to the valve inside the house, which never freezes.
To wash the chassis, I simply pull out the hose, snap it onto the undercarriage washer, rinse the undercarriage with three or four passes under the truck, disconnect the washer, retract the hose, and lay the washer down upside down at a slight angle to drain. Less than two minutes to set up and two minutes to put away.
"Slick as snot on a glass doorknob," as an old friend used to say.
