i go through periods of binging and purging daily, and then it slows down for a few weeks. one thing that has helped me keep from purging is the idea that someone might hear me. i only purge if no one is home or if i'm going to take a shower. i am TERRIFIED of being caught because my parents have questioned me about weight loss and whether or not i purge, and i always deny their suspicions. i already see a therapist so yeah, i don't see much point in it. anyway, in public i'll only purge if i can get a bathroom to myself, or have it empty. never ever would i purge at a friend's house (but i'm pretty isolated anyway).
i think i overestimate how well people can hear what you're doing through the bathroom door or something. like i said, it's a blessing in disguise, i think, but while feeling the 'need' to purge, it makes things very stressful.