When I'm cleaning the belly I stand my plane up on the spinner. While there I shoot some oil up the exhaust. Sometimes when I flip it over I drop some in the carb too. Then just hold the plane at an angle friendly to let the oil run into the engine and turn the prop several times. To make certain the oil was pulled in I hold the plane so as to drain the exhaust. Usually, nothing comes out which tells me it went as intended. I also try to turn it while inverted to lube the rockers.

Clay