Frigidaire had a remedy for that. You fill the tub with hot water, detergent and bleach and let it mix. Then spin the water out of the tub and stop the machine. Let it sit for about half an hour and then let it pump out the water. I suppose if it's bad enough, instead of passive soaking, you could hold the drain hose in the tub, moving it around to direct the stream of water around the 360 degrees the pulsator, not the tub (to reduce splashing), and let it spin to spray the recirculated water to really flush down anything on the inner walls of the cabinet.