We don't know yet where they go to the bathroom, but we finally, in this deleted scene, learn how the metahumans stashed away at STAR Labs eat: take-out, provided by Our Band of Heroes.
http://www.geeksofdoom.com/2015/05/12/the-flash-deleted-scene-grodd-lives
The article raises a good point that has occurred to me before. Sure, there are concerns over being able to restrain metahumans in a conventional prison, but has any one really thought about what it means to have these guys locked away, in little window-less cells, in solitary confinement, no contact with anyone in the outside world (and no notification to their families, friends, or loved ones), no apparent sanitary facilities, without any sort of trial or appeal or prospect for release?
Hasn't that struck anyone on the show as more than a little bit creepy? Or even just plain evil?
Well, at least they get all the Big Belly Burgers they can eat. When Our Heroes aren't too busy for a food run.