The second 400 barrel tank is hooked with a 21' long 1/2" diameter chain. Hooked over the top of the front tank and under the ears on the second tank, the same way you would use a sling on a load. I prefer 2 8' long chains, it's just less weight to carry and gives you about an extra foot of clearance room, minimizing the chances of hitting and/or bending the top rail on the tanks. But the industry standard is a 21' chain.
I love your videos! I watch them all so please keep it up!!!! But I got a quick question since I just got into a winch truck..... How do you hook the second barrel up? Great vids and keep the shiny side up!