I don't know if this has already been posted before, but I've never seen anything for it so here it is
First you want to go over to the stairs on Bravo side. The Right side where the arrows are pointing is where you want to rub up against and eventually you will only have your head, and a bit of your arms sticking out of the ground like with other float glitches. This is where you should be aimed when you start crouching. If you don't go into the ground the first time try again. Eventually you will learn how far in you have to be to do it. Remember that my aimer is centered. Finally after crouching quite a bit you should end up here. If you ever want to go down farther just press CTRL some more. Just remember this... YOU CANNOT MOVE AROUND WHILE YOU ARE FLOATING. JUST STAY STILL, AND TRY NOT TO GO DOWN TOO FAR. Thank me if this helped you at all. If a video tutorial is necessary just say so and I'll make one for you
Good luck glitching.