Heh...food never really was a big issue.  Neither were diapers (though, pull ups were a bane in the tubes, because...well, lets just say they don't contain solid waste very well and kids crawl through the tubes in one of a few ways...some crawl, some run in a squat, and others scoot on the butts.  Use your imagination).
Sickness happened, but also rather rare.
No, you don't want to know what I (or people who have worked for me) have found in them, but I will say this, in stores I ran I was obsessive for a reason about the tubes being cleaned every half hour during peak, and at least once a shift during non-peak...and the pit being cleaned out twice daily, and the balls swapped and sanitized once a week (after the weekend rush).  Things I've found are far worse than anything you've mentioned.  I will spare you the details and just say...
There are reasons we decided to remove them altogether...and you didn't list any of them.  
