To the OP:
It's pretty easy and inexpensive to do it yourself.
1. Open the drain valve on the water tank.
2. Get the "RV Blowout Plug" (Amazon, Wal-Mart, etc). Connect the plug to the city water inlet.
3. Open low-point drain.
4. Push air through the system until all the water is out of the low-point drain.
5. Close low-point and open faucet if accessible. Repeat 4 to get water out of the faucet.
6. If desired, let the trailer sit for a day or two then repeat.
7. Pour a small amount (about 1-1.5 cups) of water system antifreeze into the sink drain P-trap.
Your done! Pretty easy and quick. If you pump the antifreeze into the water lines, it gets a bit more complicated. I only did that for the first two winters, then I just went to blowing out the lines.
