MN Basement Bath Wet Vent Layout HELP NEEDED?

[StPaulJOT]

I am finishing the basement of our 100yo house in the Twin Cities. The previous owners knocked out the cement floor in the SW corner & ran waste & vent pipes for a toilet, sink & shower/tub rough-in. It appears like they were planning to use a horizontal wet vent layout, which is allowed by MN plumbing code. Unfortunately, they failed to do it correctly & I am therefore busting out the concrete once again in order to make things right for my plumbing inspector. I've have attached a drawing which shows how the city's main 4" cast iron waste pipe enters my basement. It runs straight through the middle of the area where my new bathroom will be located - underneath the cement footing for the cement block foundation wall on the west side of my house. It travels less than 20ft east under the basement floor, where it connects to the main 4" cast iron vertical "stack" that the plumbing for my first story kitchen & 1/2 bath & second story full bathroom drains into & vents thru the attic & roof. My new bathroom will have one additional fixture - a corner whirlpool. So the fixtures that I will need to run waste pipes to & wet vent per code are a toilet, shower, vanity with single sink & the corner whirlpool tub. The toilet, shower & vanity/sink will all be located inside the south wall - starting at the SE corner & moving to the west. The city water meter is right inside the west wall, so the fixture placed in front of it needs to be one that can provide the access to the water meter that is required by code. Which means the shower can't go there, but the vanity/sink or toilet should be fine. The previous owners started with the vanity/sink in the SW corner, put the shower enclosure to its left & the toilet to the left of the shower. I'm fine with this layout. Another option would be putting the toilet in the SW corner, with the shower in the middle & the vanity/sink on the left. The corner whirlpool will be located in the NW corner of the bathroom - directly in front of whatever fixture ends up in the SW corner (vanity/sink or toilet). The horizontal dry vent pipe that will need to be connected to the wet vent will be a piece of 2" PVC that will run along the south wall & connect to the home's original 1-1/2" steel vertical vent pipe that is located near the main plumbing stack. My plumbing inspector has already agreed to allow me to connect the 2" PVC to the original 1-1/2" steel pipe as it is not possible to replace the 1-1/2" steel pipe with 2" PVC without tearing my home apart. The city's main 4" cast iron waste pipe runs parallel to the south wall & is just 2-3 feet in front of the vanity/sink, shower & toilet on the one side & just 1-2 feet in front of the whirlpool's drain on the other side. My dad owned/operated an electrical & refrigeration contracting company & I worked for it for quite a bit while in HS & college. So I know what I'm doing when it comes to complying with electrical & HVAC code & have never had a problem with carpentry building codes either, plumbing code is not my strong suit. So any assistance you can provide would be greatly appreciated! I have busted out the concrete, removed the dirt & exposed the 4" main cast iron waste pipe. I know how to cut cast iron pipe & splice a piece of 4" PVC into it using flexible rubber/stainless steel couplings with worm clamps. Since I have 3 fixtures (vanity/sink, shower & toilet on the north side of the main wast pipe & one fixture (corner whirlpool tub) on the other, I'm assuming I'll need to use a PVC double wye DWV to make things work - with the 4" main line running "straight" thru the wye, the 4" wye hub on the north side draining the toilet, shower & vanity/sink & the 2" wye (or 4" wye reduced to 2" if they don't make one) hub on the south side draining the corner whirlpool tub. I'll run 4" PVC to the toilet & stub it up thru the cement floor with a 90" elbow & toilet flange. The shower requires 2" PVC pipe & trap located in a rough-in box in the cement floor. The vanity/sink will also require a 2" PVC pipe that will need two 45 degree elbows to change from horizontal to vertical where it meets the south wall, will have a 2" PVC cleanout tee above the cement floor, a 2" trap adapter tee above it for connecting the sink drain to, a short piece of pipe above that to get the horizontal dry vent above the top of the sink & then a 90 degree elbow that will allow me to run 2" PVC across the south wall (behind my 2x4 studs - between studs & cement block foundation wall) & connect it to the original 1-1/2" steel vertical vent pipe near the main stack. I know that MN code says "the water closet (toilet) fixture drain connection must be downstream of all fixture drain connections to the horizontal wet vent" & that you can't use tees in horizontal waste lines & therefore must use wyes or 45-degree elbows. Since I'm I'll use 4" PVC instead of the 3" PVC that code allows for toilets, I should have plenty of capacity & it appears like the wet vent should work well. But since the whirlpool drain is on the opposite side of the 4" main pipe than the other 3 fixtures are, I'm a little confused on how I need to tie it into the wet vent & still keep the toilet downstream from all the other fixtures. Take a look at my drawings & any help you can offer would be greatly appreciated!!!

 

[James Henry]

Your drawings are a little hard to read.