A large club/bat to the side of the head solves the problem.

The 2nd part, ban them from your country and deport the ones that are there.

The last time I was in Singapore the problem was old ex-rural Chinese pissing in the elevators so often that elevators had to have cameras installed and it became a punishable crime. Chewing gum was banned because it messes up the sidewalks. I don't think pajeet street shitters will last long in Singapore. Their video surveilance was extreme 25 years ago, now I can only imagine.