I'm not sure how it works everywhere, and really it's up to the individual inspector - but i would get what pressure i could on there, water and then boost it with air, and if you could hear that water was sputtering past the ball, i would point it out to the inspector and say "damn that ball! it doesn't seem to be working for me today!"... chances are, he would agree with you that the ball isn't doing a great job, and know that the amount of pressure you seemed to be losing was in line with what sounds/sights were coming from the ball, and know that if there was a significant issue elsewhere that it would be showing itself. Other than that, is it possible that a joint has not been glued around there and is allowing the air/water to escape? Are you positive it's coming from the ball not fitting? That's a deep main considering it's right at the house... is it possible to set the test ball at the end of the line where it dumps into the septic tank? I'm sure some of the pros on this forum will be able to provide some other suggestions...!