People trained in waterboarding would likely have two available buckets and tag team you with them. Plus they could, I don't know, apply pressure to your chest and stomach to get you to breath. Also, constantly holding your breath would result in dysfunction. I'm sure they have many techniques they use. Plus the ability to know anything you would try. Focus before, during and after on the singular goal to keep your tap shut. But waterboarding isn't the only thing theu know how to do.