Correct me if I'm wrong but the outlet size of the Eheim 1260 is 5/8" while the return of the Perfecto corner flow kit is 1". What's the best way to set this up? Reduce the "œPerfecto side" to 5/8" and use flexible tubing?
IMO, regardless of the type of pipe/tubing you use, I would suggest doing the step-up to 1" right at or as close as possible to the pump. The larger ID tubing will reduce frictional loss. I wouldn't use smaller ID tubing all the way, then step up to 1" just at the tank.