Find a stock tank and fill it with laundry detergent/water and bleach mix (not too much bleach), and submerge the seat for an afternoon. Get the water as warm (hot preferably) as you can. Then rinse the seat real good with hot water after wards. Then set it out in the sun to drip dry for a few days and/or run a fan on it to help it dry. Clean the inside of the truck real good with hot water/bleach mix. Place a bar of Irish spring in the truck under the seat when you reinstall it. Make sure the seat is fully dry before you put it back in.
