Bathroom Breaks

I think every elementary teacher must dread the deceptively simple question, "Can I go to the bathroom?". It appears that the minute "bathroom" has entered the elementary mind it triggers a physical response, and suddenly one student's raised hand becomes eight, "teacher, teacher, me too, me too!". As a teacher I groan internally, "oh no, how long is it going to take to regain focus, how long will it take them to walk down the hall, how many will decide they need a drink as they walk by the water cooler, how many will dawdle as they peer into other classrooms?" Is it better to let them go all at once and at least have the onslaught over with or one by one so that it's a long, drawn out process and any attempt at teaching you were doing is totally disrupted? Should you set "bathroom rules" about when it's ok to use the bathroom? But as every elementary teacher knows, kids have a way of taking everything you say literally and demonstrate amazingly good recall when it serves their own purposes, tripping you up over your own rules (but you said we couln't go to the bathroom during math class, when one student has an emergency). If only they were as good at remembering grammar rules!