So today I took a dry purple rag and started. It only took me less than 10 minutes. I used the rainwater to soften the muck. Then I just started wiping in a circular motion. I made a little video too put have not posted it to Youtube yet. Five minutes into the wiping; I had to go inside to rinse my purple rag. It was almost black.
I came back out with a pitcher of water to finish up the job. Just look how black the water is in the last picture. I didn’t use any kind of soap either. The purple rag did the work for me. All I had to do was make circles. In fact I could not scrub hard because I could hear the glass creak so I was afraid it might crack.