Adding an outside sink back to back with interior kitchen sink

[SabotFamily]

I'm thinking about adding an outside sink while my interior wall is open during our kitchen remodel. There's plenty of room in the wall, nothing in the way, and the outside sink drain would be within about 24 to 28 inches of the interior drain trap. My understanding is that code allows you to have two sinks on one trap within that distance. The fact that it's through a wall shouldn't matter, right?

This is in San Diego, so freezing isn't an issue, and all the plumbing for that sink is already in the exterior wall were the sinks will be back to back. Is this all good, or is there something I'm missing? Thanks, folks.

 

[Terry]

I would install a trap for each sink. And each trap needs to be vented. That can be done with a double fixture fitting, two arms, two traps.

 

[Sponsor]

 

[SabotFamily]

I would install a trap for each sink. And each trap needs to be vented. That can be done with a double fixture fitting, two arms, two traps.

Wow, thanks for the fast answer, Terry. I can see the advantages of what you describe. But I was thinking that I could leave the old cast iron plumbing alone (see photo) and just treat the two sinks like a double kitchen sink since they are so close together. Is there a reason it would be a mistake based on what you see in the photo?

 

[Terry]

Will it work? I'm pretty sure it works, both sinks on one trap. Is it code? I don't even want to think about that one.
Would it be hard to add more piping in the wall there? Yes, it would quite the job, tweaking with what you have. I understand why you are asking about the route you mentioned. Okay, on the the next post here. Do I really have to answer this one? Please no.
I won't tell anyone.

 

[wwhitney]

What was the house built, and is that cast iron in good enough condition to last for another 20 years? The latter is a question I don't know how to answer, but if the answer is no, it should be replaced now while the walls are open.

Cheers, Wayne

 

[SabotFamily]

Will it work? I'm pretty sure it works, both sinks on one trap. Is it code? I don't even want to think about that one.
Would it be hard to add more piping in the wall there? Yes, it would quite the job, tweaking with what you have. I understand why you are asking about the route you mentioned. Okay, on the the next post here. Do I really have to answer this one? Please no.
I won't tell anyone.

Ok, Terry. I think I read you loud and clear. Not necessarily advised, nor necessarily code since it's through a wall with the arm piece (even though the distance is within code). It's the old cast iron drain that scares me so I'd like to stay upstream of it for any work I do. I guess I'll forge ahead. Fortune favors the brave? It's a 70 year old house with all kinds of workarounds over the years, so at least it will all match.

By the way, I grew up in Bothell. Canyon Park area off of 39th Ave SE back in the day when that area was the country. I even worked at Monte Villa Farm when it was an actual functioning farm. Haha.

 

[SabotFamily]

What was the house built, and is that cast iron in good enough condition to last for another 20 years? The latter is a question I don't know how to answer, but if the answer is no, it should be replaced now while the walls are open.

Cheers, Wayne

The house was built in 1951, Wayne. I have no idea how long the cast iron will last, but I don't see any problems as of now. In this neighborhood, this shack is considered a scraper, so whether it will be allowed to stand for another 20 is open for speculation. (It's Shangri-La to us, by the way) Cheers to you too.

 

[SabotFamily]

Will it work? I'm pretty sure it works, both sinks on one trap. Is it code? I don't even want to think about that one.
Would it be hard to add more piping in the wall there? Yes, it would quite the job, tweaking with what you have. I understand why you are asking about the route you mentioned. Okay, on the the next post here. Do I really have to answer this one? Please no.
I won't tell anyone.

this is what I finally came up with. The outside drain is within 20 inches of the trap, which I understand is easily within code for two drains on one trap. It's also only just a little further than the original dual sink.

I tested it and the drain runs nicely. If it doesn't work out, I think I can probably just skip the outside drain and go back to basics.

For what it's worth. Thanks again -- great site.

 

[wwhitney]

this is what I finally came up with. The outside drain is within 20 inches of the trap, which I understand is easily within code for two drains on one trap.

The actual requirement is the last sentence of UPC 1001.2, https://up.codes/viewer/california/ca-plumbing-code-2019/chapter/10/traps-and-interceptors#1001.2

"One trap shall be permitted to serve a set of not more than three single compartment sinks or laundry tubs of the same depth or three lavatories immediately adjacent to each other and in the same room where the waste outlets are not more than 30 inches (762 mm) apart, and the trap is centrally located where three compartments are installed."

I guess depending on how you parse that, the "in the same room" requirement only applies to lavatories. Are the two sink waste outlets within 30" of each?

How did you connect the ABS to the galvanized (?) nipple on the cast-iron tee?

Cheers, Wayne

 

[SabotFamily]

The actual requirement is the last sentence of UPC 1001.2, https://up.codes/viewer/california/ca-plumbing-code-2019/chapter/10/traps-and-interceptors#1001.2

"One trap shall be permitted to serve a set of not more than three single compartment sinks or laundry tubs of the same depth or three lavatories immediately adjacent to each other and in the same room where the waste outlets are not more than 30 inches (762 mm) apart, and the trap is centrally located where three compartments are installed."

I guess depending on how you parse that, the "in the same room" requirement only applies to lavatories. Are the two sink waste outlets within 30" of each?

How did you connect the ABS to the galvanized (?) nipple on the cast-iron tee?

Cheers, Wayne

Connected to cast iron via what appears to be a brass male fitting. Good to see the code and details. I do realize this is an unorthodox setup. Just trying to avoid a huge main project with old cast iron. Thanks Wayne.

 

[SabotFamily]

Connected to cast iron via what appears to be a brass male fitting. Good to see the code and details. I do realize this is an unorthodox setup. Just trying to avoid a huge main project with old cast iron. Thanks Wayne.

...forgot to mention that it's definitely within 30 inches.