I am adding a bathroom to an old house. The plumbing is a mess but here is what I have. The main drain runs from west to east exiting the house to a septic system. The drain is 4". At the west end of the drain is a kitchen sink and dishwasher.
The bath about 30' east of the kitchen, will include a toilet, sink and shower. The shower is on the north wall flowing south to the drain. The sink is between the shower and main drain. The toilet is 4' east of the sink and shower. I am now planning vents. I am running a 2" line for the shower that will pick up the sink.The distance is about 12'. I am planning to vent the shower and sink with a combined system of 1 1/2" to the roof. My next decision is can i connect the 2" to the 3" toilet drain and do I have to vent the the toilet; if so how. The toilet will run about 7' to the main drain. I was thinking of connecting the 2" drain for the sink and shower to the 3" toilet drain and add a 2" vent on the 2" drain line to the attic then combine the 2" and 1 1/2" then venting a 2" through the roof. There is no 3" vent anywhere in the house.

The vent for the sink must be within 5 feet of developed length along the drain pipe from the sink trap.

The vent for the shower must be within 8 feet developed length from the shower trap.

There is no limit on the distance a water closet must be from its vent under most plumbing codes.

A 1 1/2" vent that will serve both the lavatory sink and the shower can also serve the water closet regardless where it (toilet) is located from the vent.

But always check your local plumbing code before you do anything.

WE rough our bathrooms like this. Using 2" for the shower, lavatory and vent. Good luck, Tom

In this situation can the dry vent going to the roof be 1 1/2" as long as the drains for the sink and shower are 2"?

Hi Phil

Sorry, but 2" is the minimum pipe size for a bathroom group... ;)

Mark

Mark is bang on! Run 2 inch all the way up. Good luck, Tom