Are you sure the red corduroy is going to bleed?
I would test a fabric scrap first. Drop a piece into a glass of water and watch it for 24 hours to see if any dye bleeds into the water. While it is damp, rub it against white or light-colored fabric to see of any dye "crocks". If it passes both these tests, I would still wash it in Synthrapol with color catchers but would use a short cold water wash instead of hot water. Synthrapol is a soap so there shouldn't be any toxic side effects from it. The important thing for the first wash (whether you use Synthrapol or not) is to use ***lots*** of water so any bleeds become very diluted.
And yes, the other posters are correct. At this point you would use Synthrapol, not Retayne. Synthrapol suspends loose dye particles in the water so they wouldn't settle into the elephant applique and discolor it.