We are putting a small apartment in our barn. I am trying to figure out how to vent the drains from the various fixtures.

There will be a single 4-inch drain picking up the following fixtures (starting at the most upstream part of the drain): kitchen sink; bathtub; water closet; lavatory; washing machine. The lavatory and washing machine will probably share a drain.

I know how to vent the drains from the sink, bathtub, lavatory, and washing machine, but I don't know how to vent the drain from the water closet. Do I just hook a vent into the drain at some point downstream of the elbow coming out of the bottom of the water closet?