I had a new tank and I welded a fitting on the tank for the return. Use a 1/2 p/u tube too. You don't want drink a keg with a straw. 1/2" p/u's werent stock I believe but you can get one from Mancini's or the like.
Before you install the new 1/2" pickup, snip off the vent tube and drill a hole, get a threaded nipple fitting and a nut, whalla! Or weld it on there. Easy day!