Liebig pipe size

[nelsongg]

I picked up a good amount of copper pipe fairly cheap from Craigslist. The sizes are 1.25in, 1in, .75in, .5in, and some 3/8 or ¼.
I want to make a liebig for a full keg still with a full keg thumper. I have read on other posts that the more surface area a liebig has, the better it will cool the vapor, and therefore the shorter I can make it, I think? Then I also start thinking that it will weigh too much when filled with water hanging off the side of the thumper. So can someone advise me as to how long and to what diameters of pipe to use.
Thanks, Greg