I have done that but there were 3 cows behind the trailer. Back when my kids showed there cows we made a long trip to get to a show. About 10 min before we got there we stopped for gas. All 3 of the cows had poop on them and the car wash was right there. I pulled in and we washed them all and washed out the trailer.
Everything worked fine; you just have to back off the cow at least 18” so there is a lower pressure. We didn’t have to get in a line to clean them at the show witch saved us a lot of time and headaches. But we did get a bunch of odd looks out of the people at the gas station.