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Thread: Fitting wye in existing PVC drain line

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    DIY Junior Member JLM34's Avatar
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    Default Fitting wye in existing PVC drain line

    Pretty basic question, but I've never done this so I'll have to ask. I need to cut out a section of 4" PVC and install a wye so that I can connect my new 3" drain line to the main line. I'm fine with going 3" to 4", but my question is how to fit the wye in the existing pipe. This pipe is 3.5-4 ft deep. I guess the logical thing to do is somehow dig around enough so that you could lift both sections of the main line enough to somehow fit the wye in, but I don't see this happening. That's going to be some serious excavation to be able to get a 4" pipe to budge any when it's 4 feet deep. What are my options? Thanks.

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    Moderator & Master Plumber hj's Avatar
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    You would have to excavate the ENTIRE 4" line before you could "buck" any fitting into the line. You glue to short stubs into the "Y", cut out section that length, then insert the fitting into the line using the proper "insertion" couplings.
    Licensed residential and commercial plumber

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    DIY Junior Member Widdershins's Avatar
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    Quote Originally Posted by JLM34 View Post
    Pretty basic question, but I've never done this so I'll have to ask. I need to cut out a section of 4" PVC and install a wye so that I can connect my new 3" drain line to the main line. I'm fine with going 3" to 4", but my question is how to fit the wye in the existing pipe. This pipe is 3.5-4 ft deep. I guess the logical thing to do is somehow dig around enough so that you could lift both sections of the main line enough to somehow fit the wye in, but I don't see this happening. That's going to be some serious excavation to be able to get a 4" pipe to budge any when it's 4 feet deep. What are my options? Thanks.
    Since it's outdoors and buried below grade, you can use Fernco couplings to make the transition.

    Cut out enough piping to facilitate both the wye and two 7 or 8 inch stubs glued into both ends of the wye and then reassemble with the Fernco's. The Fernco's will slide a lot easier if you spray them with soapy water.
    Last edited by Terry; 12-01-2011 at 11:44 AM.

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    DIY Junior Member Widdershins's Avatar
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    Quote Originally Posted by hj View Post
    You would have to excavate the ENTIRE 4" line before you could "buck" any fitting into the line. You glue to short stubs into the "Y", cut out section that length, then insert the fitting into the line using the proper "insertion" couplings.
    Exactly what is an insertion coupling?

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    DIY Junior Member JLM34's Avatar
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    Thanks for the reply. Still can't picture how this all fits together, but that gives me a starting point.

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    Moderator & Master Plumber hj's Avatar
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    An "insertion" coupling could be a Fernco, or a "No-Hub" coupling (although they are not REALLY made for plastic pipes), or a Pro-Flex coupling sized for plastic, or any of several other brands depending on what is available in your area.
    Licensed residential and commercial plumber

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