I worked there. The problem is that they do clean their nozzles and machines and tanks but what they don’t clean are the actual lines running the soda syrup from the storage tanks to the fountain. There’s just no viable way to do it. Sure, you can run sanitizer and soap through it but that doesn’t scrub off the black mold and it’s not exactly financially feasible to rip out all the piping from the walls and ceiling and replace it every 2 weeks.
I’m not honestly sure what a solution would be other than not using soda fountains.