Adding Softener Drain to Main Drain

Discussion in 'Plumbing Forum, Professional & DIY Advice' started by Treeman, Feb 14, 2017.

  1. Treeman

    Treeman Active Member

    Jan 29, 2010
    I am considering adding a softener drain to my main drain in the basement. What are the design specifications for this?

    - 2 inch vs. 1.5 inch
    - does the entire trap have to be above the main 3 inch drain.
    - how high does the vertical pipe have to extend above the trap......this is my major concern because I have limited space to the subfloor above. 17" from top of 3 inch drain to subfloor.
    - location in regards to the vent? okay to be before the vent on the 3 inch line.

    An example:
  2. Reach4

    Reach4 Well-Known Member

    Sep 25, 2013
    There does not seem to be much discussion of the minimum requirements for softener drain standpipes.

    That picture is not an example of good, because it is an S trap. There is no vent before the trap turns down. It could have been remedied with an AAV in the trap arm.

    Now what if the pipe had come in from the side? Could the top part of 3 inch pipe provide the venting? I don't know. Even if it were somehow allowed, I expect it would be easy to do it wrong.

    A softener usually has a fairly low flow. Typical backwash for a 12 inch diameter tank is 3.5 GPM, and 2.4 GPM for 1o inch. So 1.5 inches should be more than enough, I would think. I am confident that 1.5 inches is fine. I see no rules against 1 inch.

    This is from IPC:

    802.4 Standpipes. Standpipes shall be individually trapped. Standpipes shall extend a minimum of 18 inches (457 mm) and a maximum of 42 inches (1066 mm) above the trap weir. Access shall be provided to all standpipes and drains for rodding.​

    The weir is the bottom inside of the trap arm. The picture you posted may not meet the 18 inch rule, and if it did, it looks like it would be hard to rod.
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