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Plumbing Vent for sink pump

BillHartmann | Posted in General Discussion on October 4, 2005 08:38am

I need to add a sink pump for a basement cloths washer.

Small old house. The sewer line comes in about 6 ft off the floor.The inside drains have recently been replaced with ABS. The kitchen, bath sink and toilet (all on same wet wall) come together along with the tub drain from the oposite side of the bathroom in one area. Then the link slopes upwards toward the original cast iron vent stack.

The packaged sink pump (basically a small sewer injector pump) needs a discharge line with a check valve. That is no problem.

But it also it needs a vent line. Since air as to flow out when the tank is filling and in when it is pumping then I an air admitance valve won’t work.

I would like to tap into the “horizontal” section of the vent line, but I don’t think that is allowed. Because if there is a blockage then sewer will back up into the sink pump vent line. But I don’t see that is a real problem other than the pump might run continously until the blockage is fixed. Or the sewage might backup through the washer trap. But you would have the same problem with a pure gravity system, it is going to overflow at the lowest point.

What other options do I have.

I could go into the wall use one of the fernco “tap fittings” (not sure of what it is called but allows you to drill a hole in a pipe and makes a T). But I am real concerned about cutting the CI pipe.

The other option might be to make a loop for the pump vent up into the wall and then back down in to the horizontal part of the vent line (ABS). This would be much like a loop on a sink island vent. If I do that does it need to be above the rim of the kitchen sink the highest rim or the toilet bowel, the lowest. The vent connection will be upstream of all of the drain connections.

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  1. plumbbill | Oct 04, 2005 10:40pm | #1

    First off good catch on the "air admittance" vent not working. Most people don't catch that one.

    Yes it needs a vent size is determined by gpm's not what fixtures you have going into it.

    That vent can be hooked up to existing vent as long as you connect the vent at least 6" above the flood rim of the fixture that the vent is serving.

    drilling into cast iron although really fun is not recommended <note sarcasm>

    Get a sanitary tee & cut pipe to install --sawzall will cut pipe use lots of blades

    1. User avater
      BillHartmann | Oct 04, 2005 10:48pm | #2

      "That vent can be hooked up to existing vent as long as you connect the vent at least 6" above the flood rim of the fixture that the vent is serving."This is where I get confused.That vent is now serving the sink, vanity, toilet, and tub.Does that mean 6" about the sink (highest rim) or the toilet (the lowest). The connections to all 4 come to gether in one small area and then a comon vent line off in direction to the CI and the other direction to the sewer.And because I am concerned about how well the CI is support and breaking it even with a saw or CI cutter can I use the loop and connect the pump vent down low where it has already been converted to ABS.With the loop above the flood rim it sewage can never backup into the pump.

      1. Shacko | Oct 04, 2005 11:08pm | #3

        I think I may be missing something on this post, but the vent question is that it must be 6 in. above the flood level rim of the highest fixture connected.

      2. plumbbill | Oct 04, 2005 11:49pm | #4

        By code you can connect to the abs as long as the connection point is 6" above <that> fixture.

        You can connect to the vent pipe serving the toilet as long as your 6" above the toilets flood rim.

        The point of this is that a fixture has to flood 6" above it's own flood rim before it would flood the vent pipe serving another fixture.

  2. BryanSayer | Oct 05, 2005 12:21am | #5

    Those 'T' style fittings that I'm aware of clamp on, and I don't think I would do this with cast iron (danger of breakage) plus I believe they are also glued. But maybe there are others designed for iron.

    If you cut into the cast iron, don't forget to support it on both sides of the cut!

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