Cut into soil stack for sink

Can I cut into the existing soil stack to add a sink in basement

Basement rough in by builder has toilet and bath drain, locations are okay, also has a branch for a sink but its to far away from where I want it. Main floor toilet soil stack would be very easy to get to and sink would go about 4.5ft away, vent for upstairs toilet may be a wet vent from sink not sure if sink drains

rough hacked together layout attached

would actual have about 6 inches 90 degree elbow and then 4ft to sink
just not sure if cutting in downstream of toilet is allowed

this is all wrong,

billshack said:

this is all wrong,

Click to expand...

Not really helpful, What is wrong? I realise fittings are wrong and the vent actually does not go straight into toilet flange, its just a mashed up hack together drawing

What I wanted to know is if it is allowable to cut into the soil stack and re-vent into the same soil stack?

RedBaron said:

Not really helpful, What is wrong? I realise fittings are wrong and the vent actually does not go straight into toilet flange, its just a mashed up hack together drawing

What I wanted to know is if it is allowable to cut into the soil stack and re-vent into the same soil stack?

Click to expand...

I was also going to ask billshack the same question. It is fine to disagree with someone’s plans, but along with that you should offer some idea of what is wrong at least and better yet what is proper and the better and best way.

I’m not a plumber and we have a few here that should be along.

My fear with what you show is in the event of a clog with heavy waste the waste could be introduced into the vent line.

I would say you want it connected up above the toilet or use a cheater vent device right by the sink on a stand pipe and maybe a back flow device on the sink drain side.

Again wait and see what a pro thinks.

I think the vent has to join to the vent above the highest level of the fixtures above. Above the lav. height.

RedBaron said:

Can I cut into the existing soil stack to add a sink in basement

Basement rough in by builder has toilet and bath drain, locations are okay, also has a branch for a sink but its to far away from where I want it. Main floor toilet soil stack would be very easy to get to and sink would go about 4.5ft away, vent for upstairs toilet may be a wet vent from sink not sure if sink drains

rough hacked together layout attached

would actual have about 6 inches 90 degree elbow and then 4ft to sink
just not sure if cutting in downstream of toilet is allowed

Click to expand...

Here is a similar discussion from earlier in this forum;"moving washing machine to basement, no drain in floor"

Which basically advises too cut a 3/2/3 wye in the waste stack, as the lowest fitting, a 2", hub, no-hub or street 45, a 2" backflow preventer, a 1-1/2" reducer, an 1-1/2" 90, a santee an an AAV vent above the flood rim of the sink.

Poking around in the wall I found the the existing rough in for the sink (2") is about 6 to 7ft away from the soil stack, I would have to believe it is vented all the way to the roof as there is no other fixtures above, and it does go up through the floor. Is there any limit to how far I can run a branch vent and drain it would be the 6ft down the wall 90 deg and then 4 to 5 ft out to desired sink location

In the end I think this would be the better solution anyway if there is no issues with length

RedBaron said:

Poking around in the wall I found the the existing rough in for the sink (2") is about 6 to 7ft away from the soil stack, I would have to believe it is vented all the way to the roof as there is no other fixtures above, and it does go up through the floor. Is there any limit to how far I can run a branch vent and drain it would be the 6ft down the wall 90 deg and then 4 to 5 ft out to desired sink location

Click to expand...

If you believe its vented through the roof, what leads you to believe it does not also connect to the sewer?

Never believed it wasn't hooked to the drain, just nothing upstream. It has a tee off it that dead ends running the opposite way I want I assume that is the "rough in" for a sink. Some reason I thought it was much farther away and half put it out of my mind. I only saw it once its been hidden behind the insulation since they built the place.

RedBaron said:

Never believed it wasn't hooked to the drain, just nothing upstream. It has a tee off it that dead ends running the opposite way I want I assume that is the "rough in" for a sink. Some reason I thought it was much farther away and half put it out of my mind. I only saw it once its been hidden behind the insulation since they built the place.

Click to expand...

Then simply cut above and below the "T", revers its direction and reconnect with no-hub couplings.