Plumber didn't include drain venting in new bathroom

I paid a "professional" plumber to put in the drain system for my new bathroom that will be in the shed I'm building. I asked about a vent at the time and he said because it was just a small bathroom that I could use a "faux" vent once we put all the fixtures in after the shed was built. I didn't think much of it at the time because I trusted him unfortunately. Now that I'm ready to move forward with this project (a year later) I thought I'd research a little to make sure all is well before I put the floor in the shed. After a day of reading I've realized that there should definitely be a proper vent line and I'm angry that this wasn't done. At this point, I'm going to do it myself since paying a plumber is not what I'm feeling after the last one.

Any suggestions to where I should put the vent based on the pics? The toilet is tied directly to the main sewer line (partially uncovered toward the outside wall in first pic) and the other 3 drains connect under the toilet (in second pic). Is this easily fixable? Can I add vent without redoing the entire thing?



Thanks for your time

 

In addition to what's mentioned above, is the blue pipe I see in the 2nd pic PEX? Has it been sitting out exposed like that for a year? PEX & UV light don't play nice.

 

I never knew you could put a bathroom in a shed. How are you going to protect the pipes from freezing?

 

Good new and bad news. Bad news is this job needs to be redone properly. Good new is, everything is in easy access and it's not too extensive. This time get a licensed plumbing contractor, not a handyman.

 

If the poster is near Chicago, our friend and contributor Sewerratz is the first guy I would call.