I know. Even with chemicals down at a petrol station, you don't
get it
clean without a brush.

What you need is a special chemical called Traffic Film Remover and
ideally soft water. The forecourt machines use low concentration TFR
and should have softened water, but because the staff are too
mean/thick/lazy to top up the salt level it doesnt happen.
TRF is powerful stuff and usually only available to the trade.

Dave