I had a heap of trouble getting my belt to dye to begiun with. I finally discovered two things:
1. USE ACCETONE. You can usually get it in a can from Wal-Mart ore K-Mart. Put the girth in a large metal bowl and pour the accetone over it. The girth will probably soak up most of the accetone and what it doesn't soak up will most likely evaporate over night. BE SURE TO WASH THE GIRTH THOROUGHLY before attempting to dye!!!
2. Get a big pot and use it to dye the girth. I tried using a turkey pan in the oven and that didn't work at all so I got a large metal pot (again from K-Mart) and used that. Heat the dye/water almost up to boiling. If you bought the right girth (cotton) it WILL take the dye.