Hello Clyde,
I would start with a good laundry soap hose down with stiff scrub brush. Then use Oxi-Clean and let it sit for a little before washing it off. If you still have the spots, reapply the Oxi-Clean and let it sit longer.
Bleach will degrade the canvas if too strong or too long. I use Oxi-Clean for all kinds of stuff like that. You can over do it and start to take the color out, but it takes a lot of soaking to do that. Over night is fine for most materials. My parents had a big stain in their carpet and were going to replace the carpet because they could not clean it. While they were away for a week, I went in and used Oxi-Clean, no luck. I did it again a little longer, scrubbed the powder right into it. After a day, still nothing. I wet it down and added more power, returned in the evening to keep it wet and scrub more. I let it sit for three days, heavily coated in the powder, vacuumed it up and now they have a spot that is about three shades lighter than the rest of their carpet. At least it doesn't look dirty or stained any more. They decided they could live with that.
- Will (Dragonfly)
