[Typed all this, then realized that a picture is worth a thousand words, so pic probably covers it pretty well, but I left the details, below]

We're adding a basement bathroom. Cement has been cut out with wet saw and trench dug, have access to 3" PVC that exits through cinder clock and ties into main sanitary line under yard. Tied to this drain now:

Directly above - kitchen sink (dbl, w/ disposal) - 1.5" PVC vertical, maybe 3' sloped horizontal 1/25" copper, w/ 1.25" copper vent before the vertical drop

Above, across the room - bar sink (w/ disp), dishwasher - 2" PVC @ 45 degrees (follows slope under stairs, w/ 2" PVC vent before coming through basement ceiling

In basement, across the room - clothes washer - 2" PVC with adequate slope, AAV in-line on 2" vertical stub - this ties into sink/dw that runs under stairs before common 2" PVC enters 3" line through wall. Everything I'm describing is PVC, solvent connections except for traps at fixtures.

New fixtures:

Toilet and sink will back up to wall along stairwell. Tub is opposite. To orient, picture walls in an "L," with 3" DWV at angle, tub on one branch, sink and toilet on the other. Dbl sink is roughly over the angle of the same imaginary "L", and dw/bar sink (upstairs) and clothes washer (downstairs) are on the branch which will have sink and toilet.

Tub first - there is not a front apron; we will build a knee wall and tile it. Can I vent tub by putting AAV in-line between trap and knee wall, with an access panel through knee wall to AAV? Distance from the drain hole in the tub to the 3" PVC is about 8'. Would like to use 2" pipe, but can only find tub drain in 1.5". Would likely use reducer to increase to 2" pipe almost immediately from tub trap, then AAV would be on 2" vertical from a tee. Tub will likely reach 3" line below toilet.

If yes to that, I can focus on the other wall now. If no, then please suggest!

Other wall - toilet and sink.

Toilet will be very close to 3" drain. Sink next to toilet farther from drain. I have a 3" closet elbow with a 2" connection in the bend; is it all right to tie sink to that? Alternatives would be (1) tie sink into same 2" line that brings upstairs bar sink/dw to 3" line in basement or (2) connect sink 'below' toilet, which I guess would also make sink a wet vent for toilet?

Between toilet and 3" drain line, I'm looking at a 4-way PVC fitting (don't know name). Its 3" straight through, which would be 'toilet in' and 'drain out.' It has 2 side ports, both 2". One will be tub (hoping it can come in-line below toilet). Other could be sink, or could be vent. It is on same side as the 2" port on the closet elbow. I don't think I can use the one on the closet elbow to vent, right? That's why I'm thinking of it for sink connection, so the remaining 2" port on the 4-way can be vent.

That's my layout. I understand that AAVs are not necessarily the gold standard for venting, but it would be very difficult for me to connect to existing system or reach attic or roof. I'm trying to make full use of any other reasonable options. Thinking that sink as wet vent, plus AAV on sink and tub, am I delivering enough air to this system?

Last question (thanks if you've gotten this far!). I understand that "drain should wash vent." If I use the last 2" port on the 4-way fitting as my vent, it would come off at same point that tub drain enters, and below toilet and sink. I'll run 2" off that port to space behind stairwell wall and put 2" vertical on it under stairs, attach AAV. Does this sound like the best configuration?

Hi WVmom...

You won't like this... *UGH*! None of this is right by code!

First, you CANNOT use sanitary tee fittings on the horizontal as you have them. Here, you can use a sanitary tee fitting for a VENT ONLY or for waste piping on the vertical, but you can't use them for waste on horizontal piping, OK? Only WYE fittings are for waste on horizontal piping. So, in this case, all that work would need to be ripped out... *UGH*!

Second, no side inlet elbows allowed.

Third, I would need to know if wet venting is allowed to confirm much more, but if wet venting is allowed then you could install a 3"x2" wye, roll it above the center line of the drain pipe and then you could run full size 2" to pick up the sink and then continue upward with full-size 2" vent and connect to another 2" vent to be able to wet vent the toilet using the sink vent.

You would also need to install another 3" vent to be able to wet vent the toilet using the sink vent.

You would also need to install another 3" wye for the tub, but that would go behind the sink drain/wet vent for the sink toilet.

If wet venting isn't allowed then this gets a bit more complicated.

Questions? Let me know, OK?

Mark

PS:

I am off for a wake right now and won't be back until tonight so leave your thoughts and I'll post my response later tonight... ;)

Thank you, massplumber! Trying to get this right, I really appreciate your advice!

Searched images on sanitary tee & wye, can see difference, will need to figure out how to do. Will lose side-inlet elbow. Actually have a sweep elbow that I bought, but then discovered the other in stuff friend bought when we started this years ago w/ dishwasher install (I covered pit w/ plywood & plastic until I could get back to add bathroom; friend is no longer available).

Building inspector said I could wet vent washer/laundry tub, but I didn't end up w/ laundry tub, so used AAV in washer line. So I think wet venting is allowed.

Tub drain is at end of trench running 'down' from bottom left in photo. The closer I can get tub connection to left-hand wall, in photo, the fewer turns in the line. Anticipate digging under corner of floor visible at bottom of photo to run tub line under part of intact floor.

None of the new bathroom lines are glued, so easy to make it right. Thanks!

I think I should have replied as an "answer" rather than "comment." Will do better next time! In the meantime, more information appears as comment to massplumber's post.

Thanks

Hi again...

None of the sanitary tee fittings are allowed if you want to make this right... all those sanitary tees would need to be removed and WYE fittings used to replace them... *UGH*.

Let me know if you want me to clarify anything else, OK?

Mark

I'm off for the wake now, but will check back in later tonight!

The two sanitary tees near the wall are vertical, so that are OK, is that right? Am abandoning any further sanitary tees (the thing I called the "4-way"), but the existing stuff from upstairs kitchen, can I leave it alone?

Actaully the tees are in the horizontal from end to end. Doesn't matter wich way the side points, the tees are still in the horizontal. As mark said, only wyes can be in the horizontal (end to end). Not that it won't work, but it would not pass inspection. As long as your doing this, just as well make it right.

I understand now. If the 3" was coming down the wall, drainage from sanitary tee would run down due to gravity. As I have it, the stuff from sanitary tee could flow the wrong way through the horizontal 3" easily.

Ouch, I see why this will be a bigger job than I thought. Looks like the ideal would be to cut the whole mess off at the wall, leaving as much of the pipe as I can, then string 3"x2" wyes, one for tub, one for upstairs sink, one for upstairs sink/dw/ clothes washer, and one for new sink.

This may be more that I can DIY. The only good news is that my existing bathroom drains through a separate stack, so if I DO undertake this and get stalled, I will still have a functional full bathroom.. .

Am I on the right track? Thanks for all the good information.

Yeah, you seem to understand close enough... ;)

If you can confirm your state (I guessed it would be West Virginia?), I'll look up the appropriate codes and post on this all tomorrow night, OK?

Back to you...

Yes, I'm in West Virginia. Thanks for all your help. If I can do it myself, I will. If not, at least I will know what should be done, which will help a lot. If someone came in and suggested tearing stuff out, I would have been doubtful, but now I can see why.

Still hoping I might be able to manage, would be glad to have any further advice.

Thank you again.