I grew mine in 4" corrugated pipe and only after many months did any roots fill the tube.

I changed from 4" dia pipe to 6" dia pipe because 4" pipe became blocked with roots too quickly.

roots should not fill up a 4" pipe, no way, no chance. You might be using too few nutrients or you have plants spaced to closely. even then, blocking is extremely unlikely. I've grown many of my bigger plants in a smaller vinyl gutter with no blockage at all. It is a medium-less set of water loving roots - imagine pouring water through just perlite. It will go right through. Roots aren't more dense then that.