Rust in the cold side of exhaust manifold

[Wes]

I found a lot of rust in the manifold (Cold side) and I was able to dig a lot out as well as putting the hose to her and blasting some out. My question is,
1. What is Hottank, or Hottanking, ?
2. What is involved in hottanking a manifold?
3. What should it cost?
4. Is it worth it?
5. how long will it last etc...

Any info from your experiences would be greatly appreciated!

Thanks, Wes