Bring your own fire hoses.
Sure, the cost of a truck with a water tank will put a dent in the rally’s expenses, but sadoeconomist is an ancap so he surely must understand the idea of the people being responsible for their own sanitation.
There is no right to complain about your biohazardous materials getting washed away. If water gets on the antifas in the process of washing the piss bottles into the gutters, well it’s far more sanitary than the liquids they were throwing.
Yes, turning all protests into super soaker festivals isn’t the greatest, but it’s better than the alternative, as long as the water pressure isn’t too high. And it better be, because you’re going to have to hose down your own guys to keep them clean.
No injuries. I’m specifically talking about just washing people.
Of course, if I were in charge of the city, I’d install high-resolution cameras before the rally, get flying camera drones too, ban face-covering masks for the rally, and then fine every last one of those people $2,500 for malicious biohazardous littering (per piss-bottle) and all the mask-wearers, too.