I lined the bathtub with old towels so the racks didn’t scratch the surface. I then placed the racks one on top of the other right in the tub.
I filled the tub with hot water (enough to cover the racks), added 1/2 cup dish soap and 6 dryer sheets. I let this sit for about 8 hours. The racks will still appear dirty after this time, but the gunk has been softened.
I grabbed the dryer sheets that had been soaking and wiped the racks clean. The gunk literally comes right off with barely any effort. You can see the difference between the right and left sides. What a simple and inexpensive solution!