So, if the krausen gunk is mostly around the fore... er, top of the carboy, a concentrated soak with the bottle upside-down for a half hour will remove it. I usually add the amount of PBW I'd use for 5 gallons (3 tbsp, give or take) and only 1/4 of the water and do the upside soak with a solid stopper. Then I flip it and fill it up the rest of the way with hot water and let soak overnight.