Technically, you can wash your car at your own home in McKinney. The wording of the restriction is that you can not wash your car with a hose. I called the city water folks to be sure and they said as long as I don't use a hose I'm legal.
I have two big 5 gallon buckets that I fill directly from the tap and use those to wet and rinse the car. Not exactly convienient, but it does work.
If in doubt, call them yourself....