[Zeke]

Pool chlorine and Tide. Start with under 5% of each. Pre-wet lightly and scrub. You don't have to go ninja turtle on the scrubbing. It's about duration so don't hurry it. Do it in a cool cloudy time or evening. Keep it wet until it looks good and then use a 5 gal shop vac to pull most of your cleaning solution before hosing it into the grass.

Of course do NOT use any acidic solutions with chlorine. You could also do the chlorine with washing soda or add 1% of WS to your bucket.