Add 2 or 3 dishwasher tablets to 4 or 5 gallons of water, get it boiling, then boil the traps for about an hour or so. Then put a garden hose in the bottom of the water container and turn on the water and let the bucket overflow for a few minutes before taking the traps out. Do not lift the traps up through the nasty junk until it is overflowed out of the container.
Take em out and rinse em with the garden hose. Cold dye from leaves or walnuts will work but will take 2 or 3 weeks. It you can boil them in maple leaves, oak leaves, sumac pods, or walnuts etc. , it will dye them dark in about an hour or so,if they already have a light coat of rust.