I had trouble with some canning lids sealing (mostly metal lids with separate seals from Tattler, but often with Ball lids, too), so I have been tightening the rings immediately after removing the hot jars from the canner. I wear oven mitts or other gloves to tighten the rings. That pushes the seal onto the jar strongly and seals well.
The usual process taught for canning is to let the jars cool and let the lid seal as a vacuum is pulled from the cooling. Since I've thought of tightening the rings while they're hot, I've wondered why my new practice isn't commonly taught. It seems to work very well. I think I can't be introducing contaminants since the ring covers the seal, and the can is hot, so it has positive pressure coming out.
I've been doing this to can chicken and beef stock, processed for 25 minutes at 12 psi.