Subaru 2004 Impreza Owner's Manual page 399

Maintenance and service
Non-turbo models
4. Drain out the engine oil by removing the drain plug
while the engine is still warm. The used oil should be
drained into an appropriate container and disposed of
properly.
Be careful not to burn yourself with hot engine
oil.
5. Wipe the seating surface of the drain plug with a
clean cloth and tighten it securely with a new sealing
11-14
washer after the oil has completely drained out.
6. Remove under cover (For turbo).
Turbo models