how do i bend pvc pipe without getting the "no-longer-hollow" pinched look?

I want to bend my pvc pipe into a circle without compromising the inside shape. I have tried to do this but it continues to pinch where i want the round to be.  I have tried putting sand inside but perhaps i did something wrong because it didn't work. 

Hi this is how we bend PVC pipe.

https://www.youtube.com/watch?v=UKssOvO3nJs

nickodemus7 years ago

Thinkenstein made a great instructable on this.
Also, take a look at just how many PVC 'ibles are his (To the right of the page). This guy knows what he's doing.