I've been in homebrewing and homedistilling for some time and read a bunch of useful information about all types of whisk(e)y's and how are all of them named and such. I can't get the right information on how exactly are the barrels reused? When wine or spirit or whatever liquor was in the barrel gets taken out how exactly does the procedure look like then? Do they clean the barrel with water or steam before they put the fresh whiskey in there? I imagine you would want the flavors of whatever was previously in the barrel to have an impact on your future whiskey but there might be some trub and bad stuff on the bottom as well.
The barrels are pumped out at the winery. The barrels are probably rinsed with hot water until it's free of the gunk from the wine making process. Then left to drip dry for a while for a few days. If they are going to be used for spirits, the barrel head has to be taken off and then the barrel is charred on the inside. Otherwise, you won't get any of that smokey flavor. Wine barrels are toasted, not charred. Wine barrels go easy on the toasted oak flavor, where as whisky/scotch barrels go completely burned to almost charcoal on the inside that's how the flavor gets in there. If they just used wine barrels without doing anything, it would have a fairly weak flavor profile.