how would you go about venting a horizantal drain pipe with 6 lines coming into it. the line is 2" pvc with 1" pvc draining into it it will be horizontal with proper slope. Also this is for a fish tank not for a house. i need to know where the best place to place the vent would be. should i place one near each line coming in. can i place one at either end? also can i use smaller line to vent or does it have to be 2".