Cap full of Calgon Liquid Water Softener and a cup of Dollar Store PineSol Cleaner is all you need, along with plenty of water.
They're holding tanks unless you leave your Poo in there all season most chemicals won't do much.
2018 Chevy 3500HD High Country Crew Cab DRW, D/A, 2016 Redwood 39MB, Dual AC, Fireplace, Sleep #Bed, Auto Sat Dish, Stack Washer/Dryer, Auto Level Sys, Disk Brakes, Onan Gen, 17.5" "H" tires, MORryde Pin & IS, Comfort Ride, Dual Awnings, Full Body Paint