You cannot pressure test a tube out the tire, so it sometimes make sense o fill the bathtub to about 10" of depth and put the wheel in at full pressure and see where bubbles are forming. Know that the air can migrate between the tube and tire, but if for example, you see a stream of fine bubbles near the valve, the source is close to there.
__________________
FB
Chain-L site
An ounce of diagnosis is worth a pound of cure.
Just because I'm tired of arguing, doesn't mean you're right.
“One accurate measurement is worth a thousand expert opinions” - Adm Grace Murray Hopper - USN
WARNING, I'm from New York. Thin skinned people should maintain safe distance.