As a general rule, for things like TV antennae, electrical wiring and lighting, if it serves one lot only, it is lot owner’s responsibility. I think you would apply that idea to plumbing. How many lots does that pipe serve?
This by-law looks like it was written because owners were fed up with paying for repairs in other people’s lots. Even though it was common property, the repair might have a bigger benefit for one lot owner than anyone else.
If you think this by-law is oppressive, ask a strata lawyer to look at it. You can go to NCAT and have that by-law removed if the member agrees it is oppressive.