I know that Superman can and does eat. My question, however, is whether he needs to in order to survive or thrive? In turn, does he have to eliminate waste? If so, EWWWWWWW.

NOPE, NOPE, NOPE.

It’s inconsistent some writers portray him as a being who doesn’t need anything to sustain himself other than the sun

Some writers show that he still needs air,food,sleep like regular humans do

If superman takes a dump, Is he gonna be producing diamonds?

No to both.