You can probably search the forum and find discussion on this. Here's how I used to do our travel trailer:
1. Drain the fresh water tank and water heater (also the black and gray tanks if you didn't do that when you brought it home last time).
2. Open all low point drains that you can find. My rigs have all had at least one on the cold side and at least one on the hot side. Open a cold and hot faucet while you do this so things will drain.
3. If your water pump were not broken, you would pump it dry at this point.
4. Set your air compressor to limit pressure to 15 - 20 PSI. Apply pressure to the city water inlet while you walk around inside and open the faucets one at a time until nothing but air comes out. This needs to be done for both the not and the cold sides.
My wife and I use our hand-held radios so one of us can hold the compressor hose on the flush nipple and the other can open and close faucets. Cell phones work, too, if you're in a place where you have a cell signal.
5. Finally, pour a little RV antifreeze in the sinks, tub drain, and toilet bowl to make sure residual water in P-traps and on top of the toilet valve doesn't freeze and do damage.
Rob
U.S. Army retired
2020 Solitude 310GK-R
MORryde IS, disc brakes, solar, DP windows
(Previously in a Reflection 337RLS)
2012 F350 CC DRW Lariat 6.7
Full-time since 8/2015