My civic 98 ex has been leaking coolent from a bottom holes. At first I chagne the clamp and it stop for like 3 hours then it leak again. The next day I change the hole and it wouldn't leaking if you put the clamp a.l certain way if u put any other way it would leak again. I even took out the radiator to change the tube but no cracks or hole I could have seen. OK so I change the hole work fine for like 3 day the it leak again. I don't know if its the radiator or something else and it leaks form where the rubber hole and tube meet not in the hole

 

Post many pictures.

 

Use two clamps.

 

Apply some liquid gasket and insert the clamp. Let it dry before you pour in coolant.

 

You need to pressure test it to see exactly where the leak is, you shouldn't need any type of sealant for it to seal correctly.