In my case, I think Ritalin may act a little differently on me. Or I may react psychologically in a different way.
The urge to go to the bathroom that I feel when I take Ritalin is something that may even make me surpass "normal people" when it comes to ability and ease on these kind of situations that you've mentioned.
Basically I take the pill, sit still in my bedroom doing whatever it comes to mind, and then I feel the urge. I close myself in my mom's bathroom (which is more isolated), read a book for a couple of minutes maybe, and then I do it. Regardless of the ppl that are inside the house (obviously I am not including ppl having a party in my apartment or something like that).
Try taking some more ritalin or taking it less frequently.. At least when I do that, the med kicks in more powerfully.
But beware of the consequences, don't take too much, it's a strong med.