I have some very basic questions on plumbing. This is my first experience with plumbing. When do you need to use primer/cement vs. just regular cement when gluing pvc? Is there any harm in using primer anyway if I'm not sure? I'm using purple primer & regular cement from Oatey. I'm using this pvc from BRS: http://www.bulkreefsupply.com/blue-schedule-40-pipe-5-ft.html, as well as the regular elbows, ect. Also using this ball valve:http://www.usplastic.com/catalog/it...4Kq3FzU5OSrFyHNKlbGF0PRyWWcD3ivjVcaAjh08P8HAQ. Also on the ball valve, it is made for a slip fitting. I assume that I'll glue the pipe into the fitting. It doesn't seem to tighten like a compression fitting, or am I overlooking something?