[ahecht]

Be careful when sanding PVC -- it tends to scratch very easily. Use a very fine grit sandpaper (on the order of 800 grit).

A better solution would be to completely clean the PVC with soap and water and spray it with a primer designed for plastics (you should be able to find one in the spray paint section of Home Depot or Lowes). I've even seen spray primers sprcifically designed for PVC.

After your primer is on, you want to spray in two coats -- a so-called dry coat, which spreads some color over all the PVC but still allows the primer to show through, and a wet coat, which covers everything until the surface looks wet and shiney.