When using the black pipe I have installed barely hand tight IE almost loose fittings and after a few run cycles they are rusted and stuck (sealed) in place quite nicely. The problem with the sealants is they do not allow the water into the threads so "rust sealing" can take a longer time to burn out the sealant. If you can actually "tighten" using sealant is not a big deal either way however it is a PIA to get everything pointed in the right direction and get it installed.
Dave Neptune