Converting a house trap to PVC

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North Jersey

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I am about to replace the remaining cast iron drains in my house with PVC because they experienced an obstruction last year. The house is served by a septic system. The blockage may have arisen due to a vent stack that was converted to a soil stack back in the late 1980s without swapping the cast iron vent tee for a combo where the stack meets the main drain. Pipe scale might a contributing factor. The issue resolved itself, so I can't be certain. I am fairly confident that the blockage was not in the house trap or beyond (an air gap just upstream of the trap was clean).

I would like to retain the house trap, but I think a PVC trap might be an improvement over the cast iron. I'm planning making a new trap using a U bend from a 4" p-trap combined with two 4" street sanitary tees. I'm assuming I should look for a donor p-trap with a symmetrical bend in it. Can anyone provide any pointers on assembling one of these?
 

Reach4

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The NSPC leaves things up to the AHJ.

IMG_4872.jpeg


IMG_4873.jpeg


The existing configuration seems to have worked well for 70 years until the stoppage last summer. Do you think I should leave the XH weight trap or would a change to PVC be in order? I strongly suspect our stoppage occurred due to the soil stack pictured below dumping straight into that vent tee.

IMG_4875.jpeg
 

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At the very least, I will be installing a combo fitting for that PVC stack and removing all the upstream cast iron on the horizontal drain. I think I'll need to use a couple of 1/16th bends to offset the PVC stack so it will align with the new 4x4x3 combo fitting, which will be longer than the existing CI vent tee on its back.

Not visible in the picture is an air gap that drains directly into the PVC stack without a trap. But for the house trap, it would have allowed odors into the house. I'll be adding an individual trap for the air gap.

Finally, if I'm leaving the existing house trap or replacing it with PVC, I think I'll add a 1-foot section of clear PVC upstream of the combo fitting for easy inspection of the drain.
 
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Reach4

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Not visible in the picture is an air gap that drains directly into the PVC stack without a trap. But for the house trap, it would have allowed odors into the house. I'll be adding an individual trap for the air gap.
Good move.
 

Sylvan

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The PVC n the picture is actually a code violation as it is a TEE not a TY and it is connected to where the FAI should have been installed.

I would leave the trap alone and connect upstream. and reinstall a proper fresh air inlet
 

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The PVC n the picture is actually a code violation as it is a TEE not a TY and it is connected to where the FAI should have been installed.

I would leave the trap alone and connect upstream. and reinstall a proper fresh air inlet
I think that fitting is what caused our stoppage last summer. Seeing that tee made me wonder if the construction official inspected the plumbing. The previous homeowner (a prominent member of the legal community) paid big bucks for architectural plans and a GC to make a major addition and the attic conversion that is served by that stack.

At any rate, the 3” stack is vented at full dimension through the roof. Would it, along with a few other vents in the newer part of the home, suffice as a fresh air inlet?
 

Jeff H Young

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Prominant owner , contractor, big bucks and inspectors dont change what You have. that stack is not fit to serve a toilet maybe bootlegging in a condensate or a wet bar . probebly an honest mistake by someone new to plumbing.
 

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Prominant owner , contractor, big bucks and inspectors dont change what You have. that stack is not fit to serve a toilet maybe bootlegging in a condensate or a wet bar . probebly an honest mistake by someone new to plumbing.
I agree! The last owner tried to do things by the book and paid for inspections and professional project management, and he still ended up with some ill-advised retrofits that I will be correcting.

I suppose I was explaining why I'm not inclined to ask the construction official his opinion about the building trap.
 

Jeff H Young

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I agree! The last owner tried to do things by the book and paid for inspections and professional project management, and he still ended up with some ill-advised retrofits that I will be correcting.

I suppose I was explaining why I'm not inclined to ask the construction official his opinion about the building trap.
could be honest mistake or they didnt want to open a can of worms but dumping a toilet there is kind of a no brainer for a plumber a brand new greenhorn might not know , we all think diferantly I would have known better in my first month plumbing . A GC or inspector might not catch it . I would ask about the house trap if its required or even a good idea. I have no idea why they would like one perhaps methane thoughts may have changed on the good they do especially since you arent on public sewer
 

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I have discovered a several places where the drain system is open (air gap, missing cleanout plug, etc.), and I think the house trap is the reason we didn't smell anything. I wouldn't want to start smelling anything on the roof terrace or through dormer windows if we removed the trap. I know I could put filters on the vents, but I don't want to create the new chore of traversing the roof to replace cartridges. I like the idea of a segment of clear pipe to evaluate the flow of water through the main drain.
 

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I don't think house traps were ever required for septic systems in Jersey. I know they are currently disallowed unless the AHJ asks for them. Currently, I believe the rationale for installing them here is to avoid damage in high density urban areas where the sewer gas is particularly caustic.
 

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Another thing odd is that the vent on those arent up high . but im guessing they were trying to save running a vent all the way out the roof or that some gas wouldnt make it out. Pretty unfamiliar with house traps myself .
I guess odd they put a house trap into begin with but mighta been so common that plumbers back in the day would have thought it good to have regardless of public sewer or private septic
 

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Until yesterday, I hadn't paid attention to the upstream bends in the stack from the second floor bathroom.
As seen below, the stack enters the basement directly over a beam, a) makes a short jog with two 1/8 bends (thought it was a standard radius 1/4 bend until I got a closer look), b) enters 1/4 bend rotated down 45° and connected to a street 1/8 to make another jog before c) turning down toward the cast iron vent tee in the main drain.

Attic stack.jpg


Elbow to replaced in basement.jpg


Should I insert a long radius ell right into the 1/4 bend at a), or should I put a pair of offsetting 1/16 bends after c)?
 
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Jeff H Young

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not sure Id change it but it should be 2 45s or a long sweep at "c" I never would have done it that way due to code and plumbers just dont use a 1/4 bend like that Ive seen it but in this case little excuse for that . it probebly will never give issue but im not doing that nor any one else on here or that I know in the trade. it would have been so easy to do it right a bit annoying of someone to do that .
 

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After study, you may decide that dealing with a clog every 40 years is not so bad.
 
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