We need to move our washing machine and dryer into our garage. The garage is lower than the house. There is no water out there right now. We know we will have to run it from plumbing under the house. We really don't know where to start or how to do this. Especially how to do the drain. Help!

I assume your house is on raised foundation...

Try to put both washer and dryer as close to the house wall as possible. Run 2" waste under the house and connect to 3" or 4" pipe via "Y". Use AAV vent to vent washer drain. Pick up hot and cold water from crawl space, too. While there, locate gas line. Tap into it. Bring 1/2" gas line into garage. Dryer hot air vent should go to the outside terminated with louvered hood.

Where do you live. Do you have a sewer clean out just outside your foundation?