About a year ago, I heard of a way to make a cornie brush using a wooden dowel, some epoxy glue, and a partially disassembled wire wound kitchen brush.  This brush worked well for almost a year but recently, the epoxy gave out so I went looking for a device that would work better. 
 
Fortunately, the Minneapolis area has two Fleet Farm stores which is where I purchased a bulk tank brush.  This beauty has tons of bristles, is a perfect match to the bottom shape of a cornie, and screws onto a standard broom handle using "ACME" threads (square and course threads). 
 
Only had one problem.  I couldn't get the head and handle through the top port of the cornie.  

Drilled a small hole through the plastic head starting at the side and angling up toward the top area.   The hole allowed braided nylon rope to fit through.  Inserted a short length of rope, tied a knot at the end and use the rope to hold up the head while threading the broom handle and also when removing the head from the cornie. 
 
It is a tight fit but it works very well.  Last evening I cleaned, hot rinsed, and sanitized 6-5's, 3-3's, and 1-10.   
 
Wanted to thank the CBS for their original idea and I hope that someone reading this message tries the new and improved bulk tank version.  The brush cost about $9.00 and it does an excellent job on bottom, sides, and even does most of the lid!  Still recommend disassembly and temporary removal of dip and gas tube and valve. 
 
Rick Oftel
V.P.  MHBA