JonH – If I was you I would write a letter to the OC stating that you require a response to your previous questions within 14 days (or whatever time frame that you believe is reasonable) to enable this issue to be resolved, and to enable you to be able to finalise your renovation plans.
Under of the SSMA 2015 the OC can carry out work on a Lot to rectify defects in existing common property pipe work etc but the Act does not state that the OC can install new pipe work in a Lot.
If you want the pipe removed then the OC should be seeking alternative locations for the pipe, as was previously mentioned in a Report in 2014.
I would be advising the OC that the 3 month delay in their response has been unreasonable. I would also state that if you (a) do not receive a complete response from the OC within the time frame mentioned above, or (b) the response is unsatisfactory, then you will take this matter to mediation via the Office of Fair Trading, and then on to the NSW Civil and Administrative Tribunal (NCAT).
Be prepared to follow up on this. Your issue appears to be complex, and may require adjudication from an Authority that can Order an action(s) to be taken by the OC. The actions that you would be seeking would possibly be:
(1) the removal of the common property storm water pipe work from your Lot and the installation of the common property storm water pipe work on common property, and
(2) the making good of any damage to your Lot.
The Tribunal has the power to enforce this action under [s241].
241 Tribunal may prohibit or direct taking of specific actions
The Tribunal may order any person the subject of an application for an order to do or refrain from doing a specified act in relation to a strata scheme.