My filter's owner's manual says if using flex pipe, use the kind with smooth interior walls. We used the corrugated type last year. I'm adding 2 more solar panels this year so now is the time to make the decision whether to change to flex pvc or just use the cheap stuff. It also says use at least 1 1/2" and some of the stuff we used last year was segmented (for cutting purposes) and those segments were only 1". Anyone have any thought as which way I should go? Thanks.