Here's the process I've been using which has worked great for me. I've included the link to the full article at the bottom:
"Now, let's deal with the plumbing! If you don't have fresh water available where your rig is stored, then you need to move it. We need to flush out the plumbing system, especially if RV antifreeze was used. One possibility is to take the rig to a local RV Park or campground and use their water and sewer hookups. Hook up your water hose and fill your fresh water tank. Run your water pump and open each faucet in the rig one at a time and allow water to flow for a minute or so. If you used antifreeze, let the water flow until all color and odor is gone. Don't forget the toilet and the shower! Remember to open your gray water dump valve before you get too carried away! Turn off the water pump and hook up your hose to the city water inlet. Run some more water through the system to get that last bit of antifreeze out, then unhook the hose again. Be sure not to un-bypass the water heater until you've flushed all the lines. To put your bypassed water heater back in service, reset the valves for normal operation and make sure that the drain plug is in or that the drain valve is closed. Now run the water pump and open a hot water faucet. Once the water heater tank is full, shut all faucets and wait until the pump turns off. Listen for a few minutes to make sure that the pump does not cycle again. If the pump cycles on and off repeatedly, it may indicate a leak somewhere in your fresh water plumbing. If a leak is suspected, take a flashlight and visually inspect all the plumbing under your sinks and see if you can spot any leaks. Look carefully in compartments and inside of cupboards and storage areas until you find the drip. Fix any leaks before continuing.
Now, let's sterilize your fresh water tank and plumbing. Mix about a cup of plain household bleach in a gallon of water. Pour this mixture into your fresh water tank and top it off with the hose. Turn on the water pump and run each faucet until you can plainly smell the chlorine. Top off the fresh water tank again and let the system set for at least a few hours, longer is better. Then, drain the fresh water tank and refill with clean water. Flush the system out by running the clean water through each faucet again. Use lots of water, until the chlorine smell is gone.
This procedure will usually result in clean, odor free water in your RV. If you have problems with lingering antifreeze taste or chlorine odor, you can re-flush the system using I cup of baking soda dissolved into 1 gallon of water and follow the same procedure as above.
2007 Shamrock F19 hybrid - 2010 (22 nights), 2011 (24 nights), 2012 (11 nights)
2013 Surveyor Select 235RKS - 2012 (6 nights), 2013 (32 nights), 2014 (26 nights), 2015 (37 nights), 2016 (14 nights)