Twins – I tried to respond to your post last night but the hotspot I was using died as I hit “submit reply”; very frustrating.
I agree with Jimmy, if the cracked drainage pipe is below the bathtub of the Lot and above the concrete (ceiling) slab of the garage below that Lot, then it’s the Lot Owners responsibility to make the necessary repairs.
But…it’s never as straight forward as that, particularly when funds have been committed, to in this instance locate the source of the problem, and where that procedure and the problem itself have caused damage to Common Property.
When you say that “we” arranged for the plumber I hope you mean the Owners Corporation (O/C), because that’s appropriate in my opinion as the O/C is generally responsible to make repairs in circumstances where a fault within a Lot is affecting other Lots (e.g. the garage if it’s not part of the leaking Lot) and/or its Common Property.
So as Jimmy T advised, subject to any notations about Common Property on the Strata Title, unless your O/C has resolved how it will manage problems such as the leakage, or resolved to adopt one of the published Guideline Documents [by NSW Land & Property Information and by Strata Community Australia (NSW)] and registered a Special By-Law to reflect that resolution, it’s really up to precedent and common sense.
To me, common sense would entail making the plumbers task as easy as possible by the O/C arranging and paying for all necessary repairs to its Common Property and to the affected Lot/s, and by the O/C then seeking a pre-agreed reimbursement from the Lot Owner/s involved for the component of that cost that relates to works within the Lot/s concerned.
Even though our O/C has a Special By-Law clarifying “who’s responsible”, that approach has worked in my self-managed Plan where both Common and Private Property is involved in a repair, but you would need to make your own assessment with regard to yours