It's very similar to the usual sensations, I can feel a gentle pressure that lets me know its time to empty it. As a rule of thumb, I try to empty every 4-5 hours. If I let the pressure build up too much, it's difficult to open the valve as the gas puts pressure on it. The valve is merely a flap of skin on the inside of the pouch, it's prevents any stool from leaking out, but can be really stubborn if too much pressure builds up.