On Saturday, March 21, 2015 at 9:06:45 PM UTC-4, wrote:
The process of dry fitting, PVC pipe(s) and fitting(s) is fraught with problems. This is because the industry standards for both the pipe and the fitting socket are designed to provide an interference fit within the bottom 1/3 of the socket. This is where the solvent in the cement creates a fusion bond of the pipe and fitting. The socket of the fittings have a slight taper, to assist in rounding the pipe and achieve the fusion bond area necessary to provide a leak free, joint that can withstand the forces of the system pressure.
Sanding or grinding the diameter of either the pipe or fitting can jeopardize the quality and/or performance of the solvent welded joint.

The idea was to grind the necessary ones out and keep them for fitting purposes.
When actually assembling, you use a normal one. They only cost $.50.