JUst buy a small portion from your lfs and put them in a small shallow clean plastic tub. rinse them well. breaking up any clumps, discard any dead ones and spread them out a bit to visually inspect them so you can check for leeches and planaria, if you find these just pick them out with forceps. Secure the lid on the tub and store overnight in the fridge, next day rinse and inspect them again, then you are ready to feed your fish. scatter a few pinches around the tank and them several generous pinches just over where you want them to colonize. It help to get them to stay there if you have some detritus or well decayed organic matter from your filter media mixed in with the sand, this will also be eaten by the dragon. Repeat this every day until you use up your worms, they will live several days in the fridge. Your corys and clowns will love them and I have seen both of these burrow so deep into the gravel while going after them that only the caudal fin was visible. The reason you have to go through so much hassle is that many lfs sell wild caught worms rather than farm raised, If you get a colony established you will see the little buggers sticking out of the gravel and adding an oz of them every once in a while should allow you to maintain it. They are like tiny earth worms, fully aquatic, and most small fish will eat themselves round on them.