Hi there.
I have just rebuilt my 00 subaru impreza turbo 2000
ej205 engine
and wanted to know the best way to prime the oil system without
doin any damage.
Basically build oil pressure before starting

 

Prime the oil filter, remove crank sensor and turn over till the oil pressure light goes out.
Same proceedure for oil changes.

 

Sometimes it's a bitch to get pressure, if it takes ages a good tip is loosen the oil filter until oil flows out of it then tighten & carry on cranking until the oil pressure light goes out or your gauge if fitted shows good pressure. No matter what do not start up until the pressure is good, lots of people have ruined a new engine by not doing this. As already mentioned it good practice on oil & filter changes too.