i changed the gearbox oil on my 02 sti by removing the big nut 22mm i think on the bottom of the gearbox and filled it up with new oil,ive just read on the net that there is another drain plug by the "oil pan" can anyone confirm this and will i have to change all the oil again.thanks

 

Yes mate, there is the drain plug under the diff. - which you describe, and another in the oil pan or sump, for which you have to remove the plastic gearbox undertray to get to. Have you run the car? If not, drain about a litre or so from this - there's a chance that this will be mostly old oil - as long as you haven't run the engine (which will churn and mix the oil) then top - up as normal.
JohnD