my experience, AT vehicle:
I put a T-connector in inlet heater hose:
10mm hose go from T-connector to oil cooler, under intake manifold.
I put elbow connector near oil cooler inlet, for a smaller bend of a hose:
Drain T-connector:
I used these parts:
21311-AA170 - OIL COOLER, COMPLETE
21328-AA220 - PIPE, OIL COOLER
99078-AB330 - HOSE, WATER
21317-AA070 - CONNECTOR, OIL COOLER
80591-8010(x3) - HOSE, CLAMP
80820-6010(x2) - BOLT 6x12x12
09231-5002(x3) - HOSE, CLAMP
~15cm of 12mm(1/2") heater hose, Gates 4272-10120
~80cm of 10mm(3/8") heater hose, Gates 4272-10100
10mm elbow connector, Gates 7315-00909
17-14-17mm MR958633 T-connector, x2
22mm(7/8") hose spring clamps, x2
25mm(1") hose spring clamps, x4
some Subaru Super Blue Coolant
CARNZ, thank you for info!