The pipes in the common property floor are the responsibility of the owners corp, What goes into the pipes – in this case, probably, waste water from the shower, bath, sink and maybe washing machine – is the lot owner’s responsibility.
So if there’s a design flaw in the pipes – a kink or narrowing of some kind – that’s down to them.
But if your houshold has created a mini fatberg of, say, hair, cat litter, oil and gunk, then that’s down to you.
And if it’s backwash from another apartment, then the owners corp should be dealing with that lot’s occupant, not you.