I believe Acer is correct, your only hope is to claim on the buildings guarantee, which should still exist but if the developer has gone bust - you say it is a bank repossession from the developer - could be difficult to track down although the details of the insurance policy for the buildings guarantee should have been issued by the developer. We have had similar problems on our development, washing machines draining directly into the basement, showers with missing pipes under the tray. The owners went ahead and got them fixed. We had faults in our own apartment though thankfully no leaks.
I can't see the community being responsible for anything within your private apartment which is your property, unless any of the missing pipework is on communal property when of course they are liable for that part, if this is the case then put something in writing to the Administrator, if you don't receive a reply notify them that you are getting quotes for the work and make sure any quotes specify the amount which is for repairs on communal property, you are entitled to make emergency repairs (to communal property) if you can prove the urgency.
Otherwise it would be quicker to bite the bullet and repair the pipes, keeping all documentation in case you can make a claim anywhere.
The only other thing I can think of is taking legal advice re the bank's liability in selling you the property with faulty services, though I would think that is a long shot. Ask the lawyer who did your conveyancing if there is anything in your purchase documents that can help, and whether the buildings guarantee insurance policy details are there.
Presumably the price you paid reflected the situation. It might be worth getting someone in to check that the rest of your apartment is OK, so that you don't have any other nasty surprises in the future.
Good luck.