DWV Water Test Level Keeps Dropping But No Leaks

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Charleston, SC
A bit frustrated and hoping someone here can reassure me or help me find a way to pass a plumbing DWV rough-in inspection. City of Charleston, SC. They only allow a water test. No air or vacuum test allowed. I've never done a water test before, but understand the basics of how it's done.

Project Details - Adding a full bathroom in the front room over the garage. The rest of the house is one story on an 18" high crawl space. The closest 3" drain line was over halfway across the house, where the two existing bathrooms lead to the sewer lateral. There was a 2" which drained the laundry and kitchen which tied into that 3". So I cut out the 2", picked up the laundry and kitchen with my new 3" and ran it halfway across the house to the 3" coming the from other two bathrooms. Everything worked out great with the installation. The problem is the testing. I have 4 test tees under the house, to block off the other pipes leading into the new ones - laundry, kitchen, from other bathrooms, and the sewer lateral. Filling the system from the new vent pipe cut below the roof line.

Here's the problem. People live in this house. In fact, retired people who are always home. I can't do a 24-hour test or anything that long, since during the test there would be no functioning drain system. The few times I've tried a test for a couple of hours, the water level keeps dropping. Maybe an inch or so in the couple of hours time. Seems to slow down as time goes. I've checked every inch of the PVC pipe, every fitting, everywhere, at least a dozen times. There is not a drop of water escaping that way. The test ball and Clean-seals are all holding pressure, but there is no way I see to tell if any of the 4 are allowing a minutiae amount past them. Is there anyway to know? I'm sure there is air trapped against them, and in the overflow pipe for the tub. Could that be causing the water to drop slowly like that? I'm guessing if it is trapped air getting absorbed then it would stop after awhile, right? How long? I have the plumbing inspection scheduled for Tuesday and not sure what to say if the inspector notices the water level dropping 1/4" in 15 minutes. I'm setting up the test first thing that morning and the inspection could be within 30 minutes, or 8 hours. The only options I see to getting the air out would involve destructive testing of what is a water tight drain system right now. Any suggestions?
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