I tumble first, since I don't want to scratch my dies with dirty brass. (I don't know about you, but I usually manage to drop a few cases in the dirt, besides the powder residue, etc.). I use one tumbler, but two different medias. I clean the dirty brass with walnut hull media, and after I have resized, deprimed, and trimmed. I tumble again using less agressive corncob media. This removes whatever lube is on the cases and also cleans the now empty primer pocket. I have my tumbler on a cheap on-off timer, with only an 'off' pin installed. I just set the amount of time I want the cases to tumble, turn it on, and walk away. Once it stops, it won't come on again, even if I leave it for a week. I adjust the time based on how dirty the brass is, but generally 3 - 4 hours before resizing, and 2 hours after.