You need a bushing to go from 2" to 3/4" threaded (NPT or whatever it's called) and then the Locline just threads into that.
Sorry, I didn't realize your returns are 2", that is quite a size reduction. Although you could think about having more outputs I suppose. You could either plumb additional outputs with the pipe, or you could use Locline Y adapters (e.g.,
http://www.jlaquatics.com/phpstore/s...t_ID=pl-mp034y )