Help, I have multiple bathroom sinks that will not drain. This has been a problem since A/C guys ran a drain on the vent line in the attic. So I put a "T" on my drain under the sink & ran a vent under the sink. That did not work also. Could it be that I will have to go in the attic & re route the drainage lines away from the vents? Any suggestions or remedys would be greatly appreciated!