On Tue, 26 Jul 2011 20:35:30 -0700 (PDT), Harry K
wrote:

PVC is harmed by UV rays of the sun is is not advised for surface
use. I do use it and have pipe that has been above ground for years.
It does turn brittle however. The only repairs I have had to make is
when I forget to drain th system before it freezes.

My solar pool panel pipes are 2 inches, painted with latex? No damage
from UV so far. Years old.

The system has a "positive drain valve" (PDV) on the highest area.
When the pool pump turns off, the pipes drain to prevent freezing. The
pump comes on and closes the PDV.

The positive drain can be found for irrigation as I understand. When
the system turns off it leaks into a small dry well at the end of a
water zones.. No need to flush/ blow the PVC lines in the ground. I
don't have the irrigation version. I'm in the desert. The solar PDV
works great for the rare occasion it freezes in Las Vegas.