Basement Rough-In Advise

I have an 1911 2-1/2 storey with an unfinished basement that my wife and I are in the process of maping a layout for finishing this winter.

We'd like to build a small half bath under the stairs but have never roughed in a bathroom before. Done plenty of above grade plumbing before so I'm not afraid of the work...

I need to know what pipes to run and where to tap into the main line...

I have provided a picture of they layout of my basement with the bottom of the stairs being the bottom of the picture and the main line running under the floor in grey....

In red I have where I would like to put the toilet and sink in the future...

There is a 2" Tee coming off the main stack just behind the wall that the sink would be on so I figure I could just bring a p-trap off the main stack and drain that way... As for the toilet I need to know how I'm going to tap into the main line under the floor as well as install a backwater check valve on the toilet line to prevent a sewer backup thru the toilet.

Also I need to know what kid of venting I need... I really don't want to go 2-1/2 storeys up... can I vent to the main stack? There is another 2" tee coming off the main stack near the ceiling in the basement as I believe there was an old kitchen sink connected to it in the distant past... Now it's just capped off... Could I vent to there?

Cheers and thanks for the help guys... Feel free to scribble on my doodle to let me know where to run the pipes...

Cheers,
Jay

HOw easy this is will depend somewhat on the level of the main line under the floor. Your toilet would need a 90 then enough depth to fall 1/4" per foot before it connects to the drain line. If the existing drain line is just under the slab, you may not have enough to work with depending on its thickness. A rear discharge toilet would work, since it is starting with the outlet higher in this case. Far more selection and cheaper if you can do it with a 'normal' one, though.

While you don't have to go all the way to the roof with vents, you do need to go above the highest drain going into the pipe which probably means the sink on the second story. You can join a new vent into an existing one, and probably the attic may be the best if you don't want to go all the way to the roof with a new hole and pipe. Both the toilet and the sink require a vent, but they can be combined to one before they continue upwards if done above the sink (nominally at 42" from the floor). Normally, a drain line cannot also be used as a vent. Only once the pipe is only performing one function can you tap into it to extend a vent. A much less desirable alternative, and not allowed everywhere would be to use AAV (auto air admittance) valves for the venting.

If you decide to do it, you may want to rough in for a shower as well. Same problem with the p-trap in that case with slope to the drain. A shower requires a 2" drain line.

There was a laundry sink originally attached to the 2" capped tee near the floor that I mentioned before.... I pulled that sink out myself and it was never vented...

Anyway... I think I have enough floor to work with... how do I vent the toilet? Do I need to use a 3" x 1-1/2" Tee and bring a vent line sideways off the toilet line under the slab, up the wall and into a vent line? I've seen a strange vent made from an upside-down U shape of pipes that reattach to the sewer line to allow air to enter after the water...

There are no vents in the house, the only vent is the stack itself.... I guess that's what they did in 1911...

Since I already have an elbow attached to the bottom of the funky 4" Cleanout/Stack/2"Tee thingy... I figure I have enough to install an elbow for the toilet flange and my run to the sewer line is about 4 feet away so I'll only have to drop an inch...


It's a matter of where I attach the vent to on the toilet line and where I send the vent... I don't have one to attacht to and you're right, the highest drain in my house is my second floor bathroom sink...

Cheers,
Jay

The toilet drain needs to go through a 90-degree el underneath the toilet and in a minimum of a 3" pipe, that's fairly deep (don't know the actual measurment). A cleanout at floor level might work for a rear-discharge toilet, but not a normal one that discharges beneath the toilet.

A vent for any drain needs to go up before it can go horizontal, otherwise it can fill with waste and wouldn't provide the air path required. Any horizontal sections still need slope to them in case of any moisture (from condensation or rain, etc.) that may end up in there.

Your existing drain becomes the house plumbing vent once it is above the highest drain line. There could be some pipes in the wall that tie things together for venting, but it is possible things are all wet vented except maybe the top sink.

Usually, when adding new, you have to do that right. They won't make you change what is not being modified. This means any new plumbing you install must be to current codes. this would mean venting them properly which may mean running a new line all the way to the attic or roof.

Called a plumber... Air Admittance Valves are code here with two flavors... $8 if I'm doing it myself or $30 for some fancy one if the inspector is paying a visit...

I can save a little space under the toilet by using one of those Tees that I would put a screw cleanout on the end.... I could use one of those capped off at the unused end and use the two remaining ends as my 90-degree... I save about 1/2" that way....

Where do I attach the toilet vent? I'm going to drain the sink into the 2" inlet that's already at the bottom of the stack and run some 1-1/2" up the wall behind the sink (in the laundry room) and vent it with an AAV...

I just need to know where I attach the vent line to the toilet line... I can just run it up the wall (to the right of the stairs...) and tie into that same vent line to vent from the same AAV.... any ideas?

Feel free to scribble on my sketch to show me where to run the sewer line and vent line... don't worry about the sink... that one will be easy now that I know I can use an AAV!


Jay

It sounds like you are considering a rear discharge toilet since it is unlikely that the cleanout is submerged below the slab. You'd run the vent line from the pipe coming out of the rear of the toilet up and either connect to the other vent with the aav on it, or add one for the toilet. Note, you can't bury an aav in the wall, it must be accessable for maintenance. Run this by a plumber.

This is what I figure I'd do... where would the toilet vent come off? (Instead if a cap on the Y, could I use a 3" to 1-1/2" threaded reducer and go straight ahead towards the sink under the slap and up and connect to the vent line above the sink behind the wall...???)

would one of those 1-1/2" AAVs be able to vent a toilet or do I need to get a bigger one, or a second one...

I won't bury the aav in the wall... the wall will be unfinished on the other side and if I ever drywall the laundry room, I'll use one of those recessed access panels for the aav (looks like a bathroom exhaust cover)

Jay

I'm just going to put the bathroom at the bottom of the stairs and hide the cleanout under the vanity... (Unless that's a no no)

Jay