Just for clarification for anyone looking for ITI in the future (since this OP was awhile ago and probably already traveled) the ITI terminal is between Terminal 3 and Terminal 4. It's tiny, not a traditional terminal, more like a doctor's waiting office. It's on a side street that heads back inwards towards the tarmac and air grounds.

Not the best description, but for a general idea, MNL has kind of a layout of a "T" with the old T1 and T2 on the right side near top and in the crook of the angle, T4 at the bottom, and T3 along the left side. ITI is along this left side, close to T3. Also it's on google maps where the big Philippine Airlines water tank is, and if you zoom in you will see Island Transvoyager.