For severe cases, just hold the chick, butt first, under the faucet. The water should be tepid, not screaming hot, not cold. The poop is hard and takes a bit to absorb the moisture, but as it does, crumble the poop away.
Pat the vent area gently and apply some vasoline or olive oil. This helps in preventing future sticking issues.
FlockWatcher's recommendation was a good one. Many times, small brooder tubs/containers are simply too warm for the chicks and don't provide enough cooler space for the chicks to self regulate their body temps.
thanks for the tip! i know one of mine is getting a partial bath today... lol. I don't think its going to be too happy with me