Loophole: This could mean you lose smelling as a sense. Not that you are immune to these smells, just all of them.
its says you never have to. this could mean you never encounter a situation where you would smell these things.
what if the meaning of the wish itself is malicious, so he tries to manipulate it and ends up doing good? or the wording is not ambiguous at all?
You totally have the ability to try to make the wish not twistable, or double trick the genie. That doesn't mean you'll succeed though.
Where should this comment appear?
This pairing only
Whenever "Never have to smell sewage/manure/feces/urine again" appears
Whenever "A genie appears and grants you three wishes. Each time ..." appears