Grey and Black water tank maintenance SnowbirdInFlight, Liquid water softener and detergent is fine. Wal-Mart only seems to carry liquid water softener and I've used it. The cheapest generic is fine too. I prefer powder because I'm cheap and hate paying shipping charges (included in the retail price) on water. The water I have hydrates powdered water softener and detergent just fine. I just think liquid laundry chemicals are a rip-off - you pay more for less, and then dump it in water anyway. Just give me the powder and I'll supply the water at this end. Remember, The Geo Method will make the gunk let go, but you still have to use PLENTY of water to flush the gunk out of the tanks. The drain hole is relatively small. The older the RV the more flushing is required initially. I use a Flush King to accomplish this efficiently.