It may be that you are just lazy and hiding from the boss, got carried away reading a magazine or maybe you are genuinely constipated!?!
Any of the above can be considered 'Taking a Sit'
Tim: That was a good sit!
Tom: What do you mean?
Tim: I Must have a bit of corn stuck in the cilo!
Boss: Where have you been for the past half hour
Employee: I was going toilet
Boss: Oh, I see, you were taking a sit