i just push them too if they will push, mate if they leave their windows open, dont worry about the water, what if it rained. as long as you dont directly spray in
just dont do what a friend of mine did, it was over a conserv roof and about 30ft high, he put the brush on the window and the window opened inwards whislt the water was on, he pulled the brush back and pulled the window back to with it with the brush inside lol! whilst the water was still going and his infa red button wouldntwork so he had to run back to the van...lol! good job they werent in!!