Use of the word "drained" is surely indicative of losing all the oil?
HC, this is another illustration of how do you interpret AC 29-2C.
Since this is a test of the capability of the residual oil in the transmission to provide limited lubrication, a critical entry condition for the test should be established.
The question seems to be, what constitutes "residual oil"? That remaining after the crew have activated the switch? Was the point of switch activation considered the "critical entry condition"? Questions, but no answers.