shower drain

2 questions,

1. That should I use to clean the ABS pipe with before I solvent weld the drain to it?

2. The nockout that was on top of the riser pipe for the shower drain fell down into the trap. How do I get it out?

The answer to your first question is easy. No primer or special preparation is necessary with ABS. What I do is to scrape the inside and outside edge to remove the burring that occurs when cutting. Be sure you use ABS cement, not PVC. As for the second problem, I haven't many suggestions to offer. If you can reach it with a probe, perhaps you could use some tape on the probe.