Why so keen on getting rid of them???? They could be very useful Pokemon!!
Well, you have 3 choices really.
1: You drop them off at the Day Care before leaving Hillyard-- but the rate is extremely expensive
2: Drop them off to Prof. Ebony at the next town or before leaving Hillyard (note that they will not grow if you leave them there)
3: Have a rotating team, where you can swap Pokemon out while you carrying them. The most Pokemon you can carry like that is 8. Remember though that the two that have been rotated out cannot be used in battle. And you can only rotate them in between battles.