On Saturday, April 8, 2017 at 11:02:21 AM UTC-7, christine wrote:
I am installing a 100 lb farm sink. The specs suggest supporting
it for 300 lbs. I have...lengths of 12 gauge strut channel or .5 or .75 galvanized pipe.

Pipe is subject to buckling if used in compression, so a 2x4 would be better. The
prospect of rotation at joints means that pipe is rarely useful, and only with crossbracing ...

To be on the safe side, you could get plumbing estimates and then switch to one or two steel bay replacements for behind the wall. Steel studs behind walls support far more weight than wooden 2x4's.