Relatively inexpensive shop built under the mower deck washer.
While working a "local" (110 mile a day drive) about 15 years ago I came up with a way to wash under the decks of the 3, 5 and 7 cutting unit decks on their $35,000 to $60,000 lawn mowers.
Back then I bought the materials from a local hardware store for about $45. The material list was pretty short and was mostly just 1/2" black pipe; 1-9' Piece, 2-8" nipples, 1-4" nipple, 2-caps, 1-tee, one brass ball valve with female fittings and one brass 1/2" pipe to hose adapter.
Assembly is pretty straight forward. Bend the 9' pipe close to as shown. Attach the tee, 8" nipples and caps. Drill the holes in the top of the two nipples, I started with 1/8" holes but later drilled them out to 3/16 to decrease the pressure of the water coming out of them to prevent getting water through the blade spindle seals. Attach the ball valve to the other end of the long pipe, then the ball valve, nipple and finally the hose adapter.
To use the washer the mower operator started the mower, idled the engine, turned on the decks and remained in the seat while another employee operated the washer which was connected to a hose connected to a faucet on one side of our recycled water building. The height of cut was set at 2 1/2" so we never had an issue with a blade hitting the washer.
After the machine was washed with the recycled water it was rinsed down with straight tap water to prevent the bacteria in the recycled water from building up on the mower and turning it from bright RED to tan after a few washings.
hamman, Kster526 and BolensHorse72 have said thanks