Hello - adding an outdoor bathroom approx 40 feet from the house. Tied into the house main drain. Planning on no venting at all. Will a toilet and sink work since the house already has plenty of vents?

Hi...

Nope... plumbing doesn't work like that... ;)

You will want to install a full size cleanout just after your connection into the main drain line and then install another cleanout at the new bathroom area.

You will want to install a 3" vent through the roof of the new building as plumbing code requires it. If that simply doesn't float your boat and you won't do it then at a minimum install a 2" drain/vent for the sink as drawn below and stub that out the roof. As a final recommendation, if you don't want to go out the roof then you could install a mechanical vent (called an AAV) inside the sink vanity base. At a minimum you need to have this vent and it needs to remain "readily accessible" for future swap out should it fail, OK?

The sink and toilet MUST have a vent or the sink drain will siphon as a result of the toilet looking for air every time you flush and that will allow sewer gasses into the bathroom... a BAD THING!

Questions? Let me know...

Mark