I know I'll get some good advice from you guys because I've tried car wash and Dawn and a soft long handled brush to scrub out the remnants of Blue Heron Shit! All summer we would get to the boat and see that they would sit on the Bimini and just poop and it would run down to the mooring cover. I would hose it off as best as I could but now that it's the off season I removed both Bimini tops and really want to give it a good cleaning/scrubbing. MOST of it is coming off but there is still some that's ingrained in the fabric. Never had this trouble with our Sunbrella Bimini top or mooring cover. Any other ideas?