Basically you have to stop and find a DI, ask permission to speak, then ask to make a head call. If you're still on liaison, you'll need to be escorted by a candio. But yeah, it doesn't happen much, PT is never more than an hour, tops.Never saw anyone that made a head call during PT but for the most part the staff knows you are very hydrated. We were always told we would never be denied a head call. Once you start academics, you can use the head as often as you need too. When I made the statement about after working hours, I was just referring to OCS being somewhat peaceful/less stressful.
Only time it might be an issue would be the PRT obviously. I mention it because one candidate made a head call on his own during the PRT run, supposedly because his time wasn't good enough.
WRT BM's at OCS, constipation was an issue for a lot of us when we first got there. I just went to sick call, and they gave me something for it. It's easier than it used to be, in the old building they had communal heads, so everyone had to go at the same time. "One goes, we all go!" And like WEGL said, it's easier once you start academics.
Also, make sure to get some of that Jamie Lee Curtis yogurt at breakfast.