Cleaning plastic bags can be time consuming and it's much faster and easier to throw them away.
So let nature do the work for you. If you use garden stakes or other poles to guide your garden hose away from plants, let them do double duty.
http://www.flickr.com/photos/60961560@N00/4151150246/
Turn your plastic bags inside out and hang them upside down on the garden stakes. The rain will clean them and the sun will dry them. At the end of a sunny day, bring them inside and give them a quick wipe to reuse them or bring them to Far West fibers near SE Holgate and 17th.