Just an update. Now have a working bulk tank.
Worth had a good idea, epoxy the threaded end of the cut off bottle to a piece of 1 inch pvc. I decided to go a slightly different route. I cut off the threaded end and discovered that 1/2 inch gas black iron pipe (with tapered threads) will screw into the threaded plastic piece.
I went to to Lowes and searched and searched. CPVC, PVC, Nylon, Brass, and misc will not work. These will not "screw" into the cutoff piece. Not enough grip. Black iron and Galvanized works fines. Finally found a Schedule 80, 1/2 inch nipple, specifically "Lasco" brand. Oddly, another brand of the exact same nipple wouldn't work. Obviously tolerances aren't terribly close.
I picked up 2 of the nipples, a piece of 2 foot long 3 inch pipe, a 3 inch to 1 1/2 inch reducer, and a 1 1/2 inch to 1/2 inch bushing. I had hose clamps and clear tubing already on hand.
All pieces put together. Works like a charm. The bulk tank holds about 3/4 of a gallon of Fertilizer Concentrate. That is enough to produce about 243 gallons of fertilized water. I mounted the "bulk tank" with chain on my well house. Please over look the junk piled up.
All though this will continue to be a work in progress, it shows a lot of promise for a dirt cheap injector.