Any tips on how to install a Moen A725 Drop Ell properly to make sure there are no leaks in the wall while at the same time making sure the ell is flush with the wall and the outlet pointing down?

I have 1/2" 90 degree drop ear elbow in the wall screwed onto a 2x8 that is not going anywhere... When the wall is covered with tile, there is no way to check if that is leaking after install....or is there?

Any help is appreciated.