I actually have two questions. I'm adding a bar sink drain to an existing laundry sink drain. The drain from the laundry sink is 1-1/2" PVC, and this goes to a sanitary double wye with 2" PVC going into the floor, and 1-1/2" PVC going up to a vent. I replaced a single sanitary wye fitting with the double wye. The bar sink will have an 8' horizontal run of 1-1/2" PVC with three 90 degree bends.

My questions are:

1. Is there a minimum bend radius for the 1-1/2" PVC 90 degree drain elbows? The local Home Depot has an overwhelming selection of various PVC fittings, and I don't know the difference between them. Some are marked ELL (should that mean something to me?), and I'm sure the others are marked as something else that I didn't notice.

2. I think I need a vent in parallel with the bar sink drain. If I connect the bar sink end of the vent with a tee within 3-1/2' of the bar sink trap, how high must the horizontal section of the vent pipe be above the sink or drain? Can it be connected to the existing vertical vent pipe with a simple tee, or do I need some other wye fitting? Is 1-1/2" PVC adequate?

1 The longer the radius, the less likely anything will ever get stuck in it, and the faster the water will flow. Use the longest one you have room for. I haven't paid enough attention to be sure what the ones marked ell are. Are they also marked DVW? If not, they may be very short radius elbows meant for supply pipes. They will make poor drain elbows. Also, it may indicate they are a true 90 degrees. Drain elbows are slightly more then 90 to go from a true vertical to slightly sloping horizontal.

2 If Tom disagrees, go with what he says. I don't think you need a separate vent for each sink. You do need a separate trap for each sink to keep drain smells in the drain. PVC is a very forgiving material. It is my first choice for most uses. If you put it together without a vent, and have problems, you can always chop it open and glue in a tee to a vent. If you make the horizontal above the top of the sink, water can never run up it.

Hi Mike, (1)90 degree elbos come in a variety of flavors. Regular for water supply, DWV for drainage, a short sweep and a long sweep. Drainage does not like elbos that have short radius as they have a tendency to develop clogs. Go with DWV or a larger radius sweep if there is room.
(2) If code allows, 1 1/2" is acceptable, However we mostly use 2" in the walls and stubouts reducing to a 1 1/2" trap for bar sinks and lavatorys. To answer your question about venting your bar sink I would need more information about the vent you're reventing back into. If a major fixtures , (such as a bathroom group) discharge into the stack from above then you will need to revent back. I'm a little confused here. In one paragraph you say the bar sink drainage will be 8' long with three 90's and down below you tell me 3 1/2' from the trap to the vent. Which one is correct? Code states that the distance between trap and vent shall be 3 1/2' for 1 1/2" and 5' for 2" without having to install a individual vent. If you have to revent, you will have to connect the new vent to the one you're connecting to at least 2 inches above the flood rim of the highest fixture. The revent will tie into the old vent with a inverted drainage tee. (just turn it upside down) more questions? Click on back. Cheers, Tom

Wow. I appreciate your quick response. From both of you.

I guess I wasn't clear on the bar sink drain. From the trap it runs about 3' to a 90 degree elbow, and just past the elbow is the easiest place to put in a vent if it is needed. The drain then runs about 5 feet along a wall to the existing 2" drain into the floor. I need two 90 degree elbows to get the drain to line up with the double wye fitting. Nothing drains from above, but the laundry sink enters on the other side of the same fitting. The laundry sink drain is within a couple feet, so no vent is needed.

Is a vent required for the bar sink? It's the 8' horizontal run from the trap to the vertical drain/vent that I'm questioning. To comply with the code I think I need a vent just past the first 90 degree elbow. Am I interpreting the code correctly?

I sure appreciate your help. I had no idea plumbing was this involved.

Yor are correct.  You will have to vent your bar sink  within 3 1/2' from the trap to the new vent if the drain line is 1 1/2".  Cut in a 1 1/2" drainage tee, point it up and  connect the new vent to the existing vent   at least  2 inches above the flood rim of the highest fixture or you could run it through the roof.  The revent will tie into the old vent with a inverted drainage tee. (just turn it upside down).   Sounds like you have it pretty well together.  Good luck,  Tom