The way to test for battery drain is to set your multimeter to amps, disconnect the positive battery terminal and put one terminal of the multimeter to the battery post and the other multumeter probe onto the battery terminal you have disconnected.

this will complete the circuit again.

then lock your car and watch for current draw after approx 30sec all electrical consumers should have shut down.A certain amount of current draw is acceptable

, as long as it is very small amount, depending on the results it is possible to determine what kind of electrical consumer is likely to be causing the drain as different components will draw different amount of amps i.e upto 0.5 amps could be an interior light etc
hope this helps