Another alternative to seperating the worms from the dirt is to place a scoop of culture on a sieve, and shine a strong light from above. The heat and light will cause the worms to migrate to the bottom of the sieve, and eventually into the container below (provided the sieve has big enough gaps).
Some people also put cold water in the collecting container to encourage the movement to the coller area.
Never tried this before though, I just throw the worms in the tank dirt and all and then remove the debris at the next water change.