I am in the process of remodeling a bathroom in my home which was build in the mid 50s. The sink in the bathroom always had trouble with drainage and I have snaked it several times and it would work a little better but not for long. This sink also makes gurgle sound when it drains. This is what I have found. From the basement it has it's own 2" Cast iron drain that goes under the concrete. Towards the top it transitions from Cast iron to Galvanized steel. The steel then goes through the floor in the wall cavity. In the bathroom there is a 90 in the wall and from it is the P trap then the sink. There is no vent in this pipe anywhere which is odd to me but the second bathroom has the same configuration but never had a drainage problem. My question is this a vent problem or is this an erosion issue with the galvanized pipe or something else.

It could be both. But it sounds like both sinks are "S" trapped witch is out of code in all states. My advice?
Replace the old piping with PVC and vent your drainage system. Good luck, Tom

Tom

Thank you for your answer.

Now that I know this for sure I have one last questions. When I vent this drain I was planing on going up the wall in a different location than where it elbow for the sink becauser there is a built in Mirror above the sink but onece I am in the attick I am right next to the horizontal Vent line for the main stack which is cast iron. Is it exceptable to cut out a section of the horizonal line and piece in PVC pipe with the T to except the new vent for the sink?