I would suggest spraying a soap / water mixture on the housing and watch for a bubble.
When I installed on my Aquatica the washer went on the inside and I used a wrench to tighten slightly. less than 1/8 turn.
Problem is, you need to spray the solution INSIDE the housing!!
I suppose you could put a small positive pressure in with a bike pump and check for bubbles, but that does not mimic how the "o"rings are designed to work.
Not sure if this would produce "false positive" results:(