For folks new to fiberglass RVs, winterizing plumbing is an ominous chore with lots of things to do, and all of the 'stuff' and plumbing is mysterious, but you know that if you DON'T do it, or do it wrong you'll have real problems come Spring! If I've forgotten something, or something's not clear, chime in here members! Let's make it easy for our friends to care for their trailers!
Hopefully this thread will make winterizing your trailer a little easier.
All fiberglass RVs are obviously not identical, but for the most part they all have similar parts. It's mostly the locations of the tanks, pumps, and drains that vary. Use this thread as a general tutorial guide on how to winterize your trailer's plumbing.
When the temps are forecast to fall
below freezing for more than a couple of hours, it's time to winterize. Winterizing generally involves removing everything from the trailer that has liquids that can freeze, including the water in the plumbing and tanks. Remove all your canned goods, bottle drinks, cleaners, anything that is liquid and freeze-able.
Next involves winterizing the plumbing. It's really pretty simple, provided that your trailer is plumbed to be winterized. If yours doesn't have a water heater bypass kit, or an anti-freeze intake valve and hose already installed, I suggest you purchase them (from any RV supplies dealer) and install them. They're easy to install (usually) and very worth the time and effort.
The idea is to remove all water from the system. There are two ways to do that, first is to blow the entire system out with compressed air until there is no water vapor coming from any faucet or shower head. This obviously involves using an air compressor and a fitting that screws into the city water inlet with a schrader valve (like a car tire valve) on it for the compressor fitting. It works well provided that you ensure all of the water is out, and you have the time to do it.
The other method is to displace the water in the system with non-toxic RV antifreeze available at most hardware and RV stores. Many of the large department stores even carry it. It's a little more complex to describe, but very easy to do in practice.
First, drain your water heater. It will either have a petcock drain installed or a plastic plug in the drain hole. Open the petcock or remove the plug. Open the relief valve at the top of the water heater to let the system fill with air behind the draining water. That will relieve the 'chugging' as it drains.
If yours doesn't already have a drain petcock/anode installed, this would be an excellent time to install one rather than replacing the plastic plug.
Next, go find the drain spigot for your fresh water tank. It will generally be located near the freshwater tank somewhere, and have a short drain hose that hangs from the bottom of the trailer. Drain the fresh water tank.
While the water heater and fresh water tanks are draining, go inside and find the bypass valves located on the back of the water heater. They will be turned horizontally in line with the pipes to allow for water flow. You'll want to turn them perpendicular to the pipes (off) to prevent flow to and from the water heater. Bypassing the water heater will allow you to fill the rest of the plumbing system with antifreeze without having to pump six gallons of anti-freeze into the water heater!
After all of the water has drained from your fresh water tank and your water heater, and you've bypassed the water heater, locate the antifreeze intake line and valve located on the intake side of your water pump. It may take some hunting to locate your pump, but it will generally be plumbed near the fresh water tank.
Turn this valve to stop the pump from drawing from the water tank and draw from the hose attached to the valve. Place the end of the hose into your open gallon jug of antifreeze and turn your pump on.
You will want to systematically turn on each faucet in turn making sure that all of the water is pushed out and that pink antifreeze flows freely. Do both the hot and cold sides of each faucet. Make sure that you do your shower and that you have antifreeze flowing through your toilet plumbing as well. Don't forget your outside shower if you have one. Depending on the size of your trailer, this will usually take between one and two gallons of antifreeze. After you're done, re-set the anti-freeze intake valve to draw from the tank. That way you won't have to remember to do it in the Spring.
Once you have all of the fresh water plumbing done, it's time to go dump your gray and black water tanks. You may rinse them and dump them again if you're particular about them being cleaned. After I'm done dumping them, and they're clean, I usually open the valves for 30 minutes or so and let any water out remains in the tanks before closing the valves and putting the cap on for the winter.
Now go to each sink drain and pour a cup or so of antifreeze into the P trap. Also do the same with your shower drain. You should perform this step even if you blow out your plumbing with compressed air and don't use antifreeze in your plumbing.
Now either loosely replace your water heater drain plug or leave your petcock open so the water heater tank can 'breathe' during the winter. Close your fresh water drain.
Congratulations! You have just finished winterizing your plumbing! Come Spring, just close your water heater drain valve, open the water heater by-pass valves, fill your fresh water tank, run your pump, open your faucets, and flush the system until you get fresh water, That's all there is to it!