Originally Posted by be happy
You will have to find the low point drains valves on the outside of your unit. There will be one for the cold line and one for the hot line. You may have more than one set of valves. This link will help with that
You will also need to drain your water heater. That will take a 15/16 socket to remove the plug. You will also need to find the water heater bypass valves, turn them the other direction. Now you should be ready to either blow the water lines or put RV anti freeze in the lines. It really depends on where you live as to which one is best.
Good Luck and safe travels
While this link is a great place to go, it is also for the motorized RV, not trailers which get much less support that the other, so it may not be a good as needed. For motorhomes, we get lots of drawings that show where the lines run and all kinds of good stuff we can look to see those drains, but we are left pretty much guessing on the trailers.
One way to go is to look in all the little nooks and cubbies where they might hide a drain valve or underneath where you might be able to spot a tube sticking out with nothing on the end, so that it is a drain and then somewhere often just above, there is a valve to find!
A few big points besides finding the drains are to remember the small details. Find the water pump and make sure there is not water left standing in the small glass filter at one end of the pump. These can get installed with the filter body hanging down and that means water stays in the glass, better to turn it bottom up so water drains out of the filter!
Don't forget some anti-freeze in the black and grey holding tanks, just as cheap insurance against the super big chance of breaking a tank!
Add some antifreeze to each one of the drain traps and the stool if it has water standing. I like to leave a bit standing on the stool seal as it keep odors from creeping up and into the RV. The antifreeze is also kind of a "lube" for that rubbery seal of the stool.