I do them like this:
First and foremost,make sure your culture is reproducing. I set the food on 2"x2" pieces of craft canvas (kinda like divider material,plastic and holey). The worms crawl all over the plastic squares and through the holes etc..
Get two cups of water and an eyedropper sort of thing. Pick up the canvas pieces and dip them gently in one cup one at a time, making sure to only wash the worms off into the water....not the food, then put it back and grab another one and continue. By now you'll have a cup with a million worms at the bottom,but the water may be dingy sooo, using your eyedropper you suck up just the worms from the bottom of the cup and squirt them into the 2nd cup of clean water for a rinse. Then use the eyedropper to feed them to the fish from the clean cup.
It's not as difficult as it sounds,and it's the easiest method I've come up with so far.
Remember~ the more cultures you have,the more worms you can harvest each day. I keep over ten cultures going at all times.