+1 (more) for Water.
My experience is much like others have stated - chemicals aren't really necessary if you have a tank washer (i installed some
TORNADO Tank Flushers ) & use a lot less water cleaning/flushing our tanks now.
IMO the chemicals are only masking the odor at best....and the odor is non-existant in our coach.
The only time we've ever experienced any odor issues is when we've been "curb side" at my MIL's for 6 weeks and the tank got VERY full...and even then the only sign of odor was when we drove down the road to a rest area to dump the tank.
I installed a tank washer on each tank & a couple of QD (quick disconnects) connections that were easily accessible....i carry a short length of hose w/ the matching QD fitting - my short length of hose has an on off valve on it - just connect the hose to the water supply and let it run for a couple of minutes.
