[Mark N.]

I always sanitize the system 3 times each season: Once before storage and once during the summer, and again before winter storage. It's cheap, and easy insurance.
I have used Sodium dichlor for years, so I thought I would include a few pictures. Sodium dichlor is cheaper than bleach, safe, easier on plastics than bleach, a LOT less messy than bleach and stores easily. There is not a single downside to it compared to bleach.
The steps I use:
1.- Drain the hot water heater and close the drain again.
2.-Hook the fresh water fill hose to the fill port.
3.-Fill the water tank about 1/4 full and turn off and disconnect hose at the source.
4.-Dump about 1-tsp. Sodium dichlor into the hose.
5.-Finish filling the tank.
6.- Turn on the pump, open each valve in the trailer and let the treated water run for a minute or so. Don't forget the outside valves and the low-point drains. I fill the hot water heater with treated water. Contrary to popular wisdom, the temps. in a hot water heater are NOT enough to sanitize. That requires 165 degrees.
7.-Let it sit for a few hours (Or overnight if you wish, it certainly won't hurt anything.)
8.-Drain the tank, refill, flush out each line for a few minutes, drain a final time and you are done!
I have included pictures of the product I use. I use it in my hot tub, and I believe it was about $10. If using it for RVing only, a 1-lb. bottle of Sodium dichlor should provide over 100 tsp. doses. That's about 9 cents per tsp.!
The accepted rate is 1 tsp. per 100 gals. of water. I usually double that because it is soooo cheap, and it won't harm a thing to double the dose.
I have included a picture of a test strip showing the high chlorine concentration this tsp. provides in my "full to the top" fresh tank. Plenty concentration for sanitizing. You DO NOT need to buy test strips, I just wanted to show you that such a small amount works fine!
A small tightly sealing and labeled pill bottle full would last you for about 3 seasons doing it even twice a year! At $10 dollars per bottle, that is about 18 cents per year, of Sodium dichlor.
Remember this stuff is as safe as bleach, and a LOT easier to handle without spilling. Just keep it away from kids as with ANY chemical.
(As a final step, though not required, I treat the chlorinated water in my tank with another chemical I have on hand, Sodium thiosulfate, to neutralize the chlorine before I dump it. I know most people just send it down the sewer drain. I alwas just let it drain into my gutter in the street, so I make sure it is chlorine free before doing so, my storm drains around here end up in rivers, and chlorine is really bad news for aquatic ecosystems. Sodium thiosulfate is totally dirt cheap and totally safe. You can eat the stuff. (In fact, many people do for health reasons!)img]http://i1378.photobucket.com/albums/ah91/mark_nixon1/Mobile%20Uploads/20151006_110115_zpshepytavd.jpg
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Thank you Rain Ducker.