Looking for expert feedback on my proposed drain plumbing arrangement.

[Sealflipperpie]

The first image shows my new proposed DWV renovation for my main floor and basement bathrooms. New pipes are in green, while existing pipes are in grey. The second image shows the existing arrangement, with red indicating what is to be demolished, and grey is the remaining existing pipe. All pipes are either 3" or 1.5".

I'm mainly looking for confirmation or feedback on whether or not my venting arrangement works, and because my understanding of wet venting is poor, I'm wondering if there's any opportunity to simplify things with wet venting? The basement vanity sink was previously on a AAV, and although not to code, I haven't pulled a permit and will not be subject to inspection, so I'm fine with keeping it that way unless someone can't point out a relatively simple solution? Tying it directly into the nearby stack wouldn't work with the tub drain above correct?

Just for some background context, this is a case of the while-I'm-at-its after gutting my flood damaged basement and installing a perimeter drain system. I also took the rental jackhammer to my bathroom floor to see if I could lower the toilet and tub drain so the new bathroom isn't raised on sleepers with an already low ceiling height. Fortunately theres plenty of vertical height to work with to achieve that goal.
The main floor toilet also crossed perpendicular to, and below the joists and ceiling. I decided to add a new drain/vent stack to pick that up on the opposite side. It will just cross one joist now, which will be notched or severed, but its above and parallel to the bathroom wall, so it will be supported by the wall.

This is also the time to install sewer backup mitigation. I initially planned to install a mainline backwater valve, but upon discovering my sewer line is 3" with a 1% slope, and options for 3" backwater valves are very limited, and not retrofit friendly, I decide to merge the basement tub and toilet and protect that branch. Future me will just have to figure out how to make an access hatch in the finished floor. The vanity and laundry sinks will likely get above ground backwater valves if there's space. They end up close to flush in height to the next upstream manhole cover in the road.

Thanks for looking!

 

[Sylvan]

The first picture looks great. Why a backwater valve????

 

[Sponsor]

 

[Jeff H Young]

the green system, has a wrong wet vented system between floors for the laundry sink , a dry vent below floor in basement , and no vent or improper vent for upstair lav.
red system main vaity is un vented and a illegal wet venting of bath tub in basement it must not utilze the laundry sink drain as the vent.
not huge fixes but major code violations in my view you arent inspecting so its your opinion on what matters and what dosent Id probeblly use an AAV in a pinch if not legal but i wouldnt follow these drawings .
sorry i didnt read your post it was too lengthy for me but hope I helped some

 

[Sealflipperpie]

The first picture looks great. Why a backwater valve????

I did a bit of DIY surveying with my laser level and measured the next upstream manhole cover at the street to be 30" above my basement floor, so I'd be at risk of sewer backup. Initially I planned to install a mainline backwater valve, but available options for my 3" sewer line and, and compromising the 1% slope had me reconsider. I decided it would be safer to protect the 2 lowest fixtures as I was replumbing the drains anyways to lower the fixtures to not have to put the new bathroom on sleepers. The bathroom and laundry sinks will have BWVs installed above ground, but I hadn't shown them.

 

[Sealflipperpie]

the green system, has a wrong wet vented system between floors for the laundry sink , a dry vent below floor in basement , and no vent or improper vent for upstair lav.
red system main vaity is un vented and a illegal wet venting of bath tub in basement it must not utilze the laundry sink drain as the vent.
not huge fixes but major code violations in my view you arent inspecting so its your opinion on what matters and what dosent Id probeblly use an AAV in a pinch if not legal but i wouldnt follow these drawings .
sorry i didnt read your post it was too lengthy for me but hope I helped some

Thanks for the feedback. The image with red is the existing plumbing, and it's certainly a mess. The upstairs vanity sink drain has even backslope before the stack.

I realized the vent issue with the laundry sink, I'll be tying it into the vent line come from the basement toilet and bath. The existing bathroom vanity sink had an AAV on it, and I didn't think I would have space to vent it properly, but looking at it again, it should be doable, so it will get a dedicated vent tying into the main stack above the upstairs tub drain.
I haven't pulled a permit and it won't be subject to inspection, but this is certainly the opportunity to do things right, and avoid any potential red flags when the time comes to sell.