1995 Holden Commodore coolant system

Engine Cooling problem
1995 Holden Commodore 6 cyl Two Wheel Drive Automatic

We have a 1995 commodore holden estate car that has a leak in the cooling system. It is not in the radiator but in the pipes somewhere along the line. We need to know how to drain the system (which tubes to disconnect near the radiator)so that we can flush it out before putting a metallic seal up through the system to hopefully block up the leak.
We've taken it to an auto shop already and they said this was probably the best bet as to repair it they may have to replace the whole tubing lines which would cost 2 grand which would not make sense as the car isn't worth this much.
We've undone two pipes all ready but these seemed to be oil lines of some sort so we don't think it's these ones.
Any help would be appreciated.