I went from memory on the above procedure and found my file and this is what I did and used. Dr. Oscar Gaddy is the one whose procedure I followed, but the etchant he use is different. The PVC tank is 3" in diameter still 36" tall but the fill mark is at 31".

Radio Shack Etching Solution 16 ozs.
Container is 3” dia. x 31” high equals 121.42 ounces or .95 gal. (volume)
Add 16 ozs. of etching to container for a 15% mix of solution to distilled water for a 5 second etch then rinse immediately in water and card. Repeat rusting and etching to your desired finish.
121 ounces minus 16 ounces equals 105 ounces.
105 ounces of distilled water is needed together with the 16 ounces of solution to bring mixture to level of 31”. This gives a ratio of 15.75 ounces of solution rounded up to 16 ounces
15% (.15) x 105 = 15.75 ounces)

Make sure you put rubber stoppers or wooded plugs in chamber side and rubber stoppers with bent copper tubing in choke side when boiling and not just rubber stoppers in or else they will blow out and you will rust the inside of the barrels.
In etching you stoppers in both ends.

Sorry for the mistake