I'm planning on framing/roughing in the plumbing for my basement bathroom. I wonder if I need to add a vent for my tub. It seems unusual, but I'm not sure. Obviously it would have to be connected before the P-trap under the tub. The home was built less than two years ago.
The dotted line of the plumbing under the slab is my suspicion based on what I can see. If the pipes run as I suspect, the line to the tub would meet the other dotted line after about 5'6".