As simple as it sounds, you have about 16 hours in which to twiddle your thumbs, watch some paint dry, or whatever you feel like. During this time, don't even think about touching your extraction, and make sure it's in a dark place. Light has a nasty habit of destroying salvinorin-a in solution. The purpose of this step is to let any sediment such as tannins fall out of the leaf which are hard to extract later on.
After the 16 or so hours are up, you may pour off the remaining liquid into the original saucepan, provided you emptied out the powdered leaf earlier.
What's the point of this step? If the tannins/tars fall out of this step how do we isolate/remove them from the solution? You say to "pour off the remaining liquid into the original saucepan, provided you emptied out the powdered leaf earlier" but doesn't this liquid contain the tannins/tars? Doesn't make sense to me.
When the evaporation is complete, you should be left with a load of black gunk on the inside of your container. This is as far as most people get with their extractions and is the reason why the end result is a black sticky mess. That's ok for about 5x or 6x extracts, but any stronger than that and it becomes unsmokable.
Isn't the black gunk the tannins/tars? If so then they weren't removed in the previous step and so what's the point of the 16 hour waiting period?
When your black gunk is completely dry, you can scrape it out of your container and place it into a tall, narrow container. To this, add 50ml or so of naphtha. The naphtha dissolves the green/black waxes but leaves behind the salvinorin-a. After you add the first lot of naphtha, allow the container 30 minutes or so to settle, then pipette off two thirds of the naphtha and discard it. Repeat this process at LEAST 5 more times until your salvinorin-a is no longer a black colour. If you keep washing with naphtha, it will eventually turn white, however that kind of purity isn't necessary for making 10x extract. If you were making something like 40x or 60x (not recommended), then the higher the purity, the better.
After the last naphtha wash, remove two thirds one last time and this time, allow the naphtha to evaporate off, leaving you with relatively pure salvinorin-a. DO NOT try and smoke/ingest this, as even a tenth of a milligram can be too much for some people.
Again, it's fine that the naphtha dissolves the tannins/tars/waxes but how are we separating them from the salvinorin-A? If we are piping out the solution aren't we losing the s-A as well? If not, why not?