I use 1/2" (ID) Schedule 80 PVC (grey), the kind they use for irrigation system above ground risers. It is heavier than Schedule 40, but is stiffer. Schedule 40 (white) will work but stiffness varies. Try to find the stiffest you can.
I found the 1/2" X 48" riser at Home Depot.
http://www.homedepot.com/h_d1/N-5yc1...atalogId=10053