tricky drain location - MN

[stever1]

Need some assistance from the experts. I'm adding a master bath, complete with a new slab and frost free footings (20" thickened edge). the 4" main to my septic runs underneath the new addition. The location for the new tub puts it almost vertically above the 4" main and near the edge of the addition, which I think means I need to run the 2" shower drain back toward the house. What's the best way to bring the tub drain into the 4"? Below is a rough diagram



recommendations?

[Terry]

The tub will need a vent, and the shower will need a vent.
If the center of the drain is over the 4" line, you can offset your tub drain with fittings to the side.

Anything coming off the main line horizontals will need to be wyes.

Between the p-trap and the main line, you will need a vent. Otherwise, water running down the main line will siphon the p-trap.

[stever1]

thanks! I do have a vent on the 3" line. the main is several inches below the tub drain. should I bring it to the 3" line as long as my overall length is less than the 5' and wet vent (I think that's the max length??) or would you bring a second 4x4x2 wye to the main?

[hj]

Just because it is NEAR the main line does NOT mean it does not need a vent, any more than having the milk carton near the refrigerator does not mean you have to put the carton inside. In addition, "having a vent on the 3" line" does NOT necessarily mean you have vented the shower properly. In fact it could indicate that it is NOT vented. You NEED an individual vent, but HOW you run the piping is something we would have to be there to decide. We cannot do it with just your drawing.