The new 4" test ball is letting water past, very slowly but enough to invalidate the hydrostatic test. I can see every joint but not the test ball (it's in a sealed wye) so I know it's the test ball. I've drained and repositioned plug three times. It's a little better but still leaks slowly. So what do you think of slathering some rectorseal or something else on the plug before inserting? Might harm the rubber? Any other ideas?