Crouching H hits OTG and gives you a hard knockdown but you can't cancel it into anything other than standing pipe.
As soon as you finish an air series, hit cr.H as quick as you can and cancel it into pipe (it won't hit, just whiff it), then hit another cr.H. You can't wait very long after you finish an air series, I think its something to do with the knockdown animation that the opponent goes into when they hit the ground after j.pipe or j.S in an air combo. It has to be quick in order to get two OTGs.
This move really shines with assists though, with Frank's shopping cart assist you get a pretty much untechable corner reset with anything into launcher, j.MMH(S or pipe), cr.H and Frank assist at the same time, standing pipe, cancel into hoodlum launcher H. Some characters can escape this, others have no choice but to be TOD'd.