I used Flex Seal to seal around the flange of a new vent stack on the roof a relative’s house some years ago. No leaks.
But a few days ago a teen brought his 29’’ tube to be fixed as it was leaking, which normally is easily patched (having done hundreds on the sidewalk by the grace of God), but with this one someone try to patche it with flex tape. Which does not work at pressure since it cannot stretch enough. Worse than using Super Glue or anything other than rubber cement (Slime 1050 best for price and quality).