I put mine in a large plastic cup, cover with water, and add a few drops of dish liquid. Pop it in the microwave (Oh, the shock, the horror!!! Metal in the micro?!?! No damage done so long as they are covered by the water) for a few minutes, let sit until cool enough to handle, and rinse. Voila!
microwave method! Works every time!! Make sure you cover the tips with at least an inch of water with a couple of drops of Dawn detergent and keep them in for 1 minute.
I clean mine using 2 wilton grid-style cooling racks, sandwiched together and secured with bulldog clips. I lay one rack across my sink and put the tips in the 1/2" grid holes, using only the center 1/3 of the rack - decorating "ends" down & leaving spaces between them like a checkerboard. If your sink is too wide, you could lay the rack across a cake pan. The other rack is placed on top and then they are secured together with the bulldog clips. I flip it over (decorating ends up) and using my sink sprayer, I spray the outsides with the hottest water possible. All the icing melts out and falls into the sink. Then I flip it over again and rinse the insides. The tips never fall out. I stick the whole thing into my dishwasher. They come out sparkling every time.