Trap for furnace condensation?
While you are waiting for the plumbers to get to this question, I can make an educated guess that they will probably advise closing up that wye and finding another method for the condensation water.
They make condensate pumps that take water collected from the A-coil area then pump the water to a sump pump or some other acceptable place.
Either that or a stand pipe system to avoid big problems in the event your building drain clogs.
Was that picture you posted behind drywall or was it exposed already?
Last edited by rselectric1; 10-18-2009 at 06:47 PM.