That hole is there because if your water seal is bad, it can let water leak into your case and contaminate your oil, causing damage. The water is draining out the hole instead of into your case. Get the seal replaced ASAP.
Are you talking about plugging up the weep hole???? I hope you aren't because that would be very, very bad. That hole is there for a reason. When the seal starts going, the water is either going to come out that hole or go into your engine.