How do you test for drain, is this the correct way before I do it?

1. Put multimeter in 10A DC mode
2. remove negative cable lead off the battery terminal
3. touch one end of the multimeter probe to the negative cable lead
4. touch other end of the multimeter probe to the negative battery terminal

So ultimately your measuring the current running through the negative terminal on the battery between the vehicle and the battery for any drain? and if its above 50-60mA at or below your fine (since the computer uses some drain anyway when car is OFF)

And if you over this 50-60mA you may have something draining too much current when vehicle is OFF and thus draining your battery overnight?