If you have access to the run of PEX from the T to the washer hookup then cut it somewhere in the middle of the run and cap it. Then take the capped stub and find a way to fix the capped end higher than the T fitting. Water will drain out of the tube when it loses pressure while you're winterizing it.
Before you sell the coach just remove the cap and use a coupler to put the cut pieces of hose back together.
If you only have access to the T then remove it and replace with a straight coupler.