The copper in pipes ( type M Red copper ) is 99.9 percent pure.
>- Will alligator clips be effective enough on one side and RCA jacks on the other?
I do not recommend either. Use only good quality, instrument grade cable, not coiled, solder to the inside of the pipes, and connect with Banana plugs ( the same type of plugs that connect to a DMM ).
I use 3/4 dia but 1 inch dia would be more comfortable for some and actually provides better contact area.