I am a condo owner. I had to have a plummer install a complete plastic bath drain because my drain was draining into the condo below my condo. Am I responsible to pay to fix my work and my neighbours.

Most Condo Docs stipulate that that if the leak's in the confines of your unit then it's your responsibility and you are responsible for any damage to your neighbors unit due to that leak. The exceptions are if the leak occurred in a drain line that's used by the building, (common area), but sadly that's not the case here. Regards, Tom