Sasha writes:

He rejected my work due to
several problems to his view:

In many places the plumbing permitting and inspecting is run by the
plumbing trade itself in a confederacy with the local government, and has
the primary mission of forcing you to hire their overpriced and entry-
restricted tradesmen, which is partly kicked back to the local pols. If
you insist on doing work yourself on your own home (as is a codified right
in my state), you will, despite the legal entitlement, be subject to
various impediments, such as bureaucratic delays, excessive paperwork and
plans not required of the trade, and (as you seem to have discovered)
arbitrary and capricious inspections and interpretations of the so-called
and chimerical "code".

There is a bona fide purpose to building codes, but they are also in many
places tools for a kind of petty political/economic tyranny.