On disposing of syringes some good advice is to put them in an empty bleach bottle. These bottles are considered toxic so the sanitation workers will dispose of them in a special way, mostly incineration. But if you want to get rid of them with no real hassle you can bring them to a hospital in a container that says biohardous material. Remember that you can get fined up to 50,000 dollars for ill-proper disposel.
So good luck and happy cycling
Lord_Suston