I don't do anything to the barrels in between beers. Pull one beer out, flush the barrel with CO2 (to avoid oxidation from splashing), and rack the next beer in. I suppose I could dump out the dregs of the previous beer before racking the next one in, but I don't. I now have 6 beers and meads which have been in Woodinville barrels, and hope to have a couple more before Philly. Nothing but goodness.