This might be worth a read and a try!! The GEO method for cleaning out your tank! I have emptied and now refilled ours with some Borax (water softener) and some washing soda (arm and hammer product) and some bleach to see if this will do the trick.
2 legs-Trev, Sue, Alley, Zac
4 legs-Zoey, Freddie, Angel, Oliver, Sweet Pea and Rango
2008 Jayco Jayflight G2 31BHDS
2012 Dodge 3500 Cummins Diesel, Crew Cab/ Short Box