Several of the people that camp around us swear by putting a cup of water softener and and a cup of fabric softener and about 5 gallons of water in each black tank(then drive it around) when it is new to coat the sides of the tanks. I have no idea if this works or has any benefit. One thing I would suggest is odor control packets/liquid for both black and grey water tanks to help control the odors(both can be found at WallyWorld). Happy camping.
2012 Sandpiper 365SAQ weighing @ 15k, Onan, 2nd air, slide toppers, TST
2013 F350 6.7L Lariat 4x4 CC DRW,Viair 1007, Ride-Rites, Edge CTS, B&W
2001 Chevy 3500CC DRW 4x4, 8.1L, 4.10 gears w/ Detroit TrueTrac
2001 Ford Excursion Limited 4x4 7.3L,V/B Spring Mod, ProComps, Hellwig Swaybar, & other 'Necessities'