After a day of offroading and mudding in my jeep, I would go to the self service car washes to clean mud off. I used the brush on the paint. I wouldn't do it with the truck, but the jeep was different. It had scratches all over from brush and trees on the trails, so I wasn't too worried about the foam brush.

 

I would NEVER use the foam brush, it's not that im worried about the foam brush, it's that im worried about what people scrubbed with the foam brush.

 

I always pressure washed the brush out before using it. But I still wouldn't use it on a new vehicle.

 

Reminds me of the shared soap in the shower advice I heard from a high school coach one. He said you should start soaping your head, working down to your feet, but you do your but last for obvious reasons. then you put the soap back in the soap dish for the next student to use.