there are lots of variables to your question. If it was winterized like most people do then YES, you will need to open the cold water inlet and open the hot water output and close the bypass valve on the back of the water heater. If you have a filter, then you will need to drain the antifreeze from that and from the water lines in the trailer. Flush all the water lines with fresh water. Most people then sanitize the water lines by filling the water tank and adding bleach. If you trailer has a antifreeze pick up line, then you will need to put the pump valve back to the position so that it will draw from the tank. Run water from all outlets until you smell the bleach at each location, then let sit for 4-6 hours and flush all the lines again.
I would suggest a you tube search on dewinterizing, there are many videos available that will demonstrate how to complete the job.
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