Go to the local 99 cent store and pick up some 'The Works' toilet bowl cleaner. That and Tide or Cheer laundry detergent. If they haven't soaked in too deep the works will do well, laundry soap a few times, scrubbed in, hose off. Same with the works, spray it on the stain (works well with rust also on concrete),let it work, you'll see a vapor, hose it down.
"When I was younger, I could remember anything, whether it had happened or not." - Mark Twain