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Hi,

We are remodeling our house and have the opportunity to start our laundry room from scratch. All of the L2L systems we’ve seen drawings of use an AAV to vent the grey water line going to the landscape. It seems most of the drawings are to retrofit an existing laundry room. If I start from scratch and can install any necesssary venting within wall, etc, I’m assuming I can just install a standard vent that goes out the roof? Is this correct? The AAV isn’t strictly necessary. You just need to have a vent (whether its AAV or not), correct? I’m assuming the AAV is just particularly easy to install and retrofit.

Second, if I can use a non AAV vent, then could I just tie back into the vent for the line going to the sewer, so I’m effectively using the same in wall vent to vent both the sewer and the greywater line? The greywater line should vent properly to the vent, because the sewer line would be blocked with a p-trap. I’m a little worried though about the sewer line, because in theory the vent may activate, but it also may produce suction on the grey water to landscape line, and draw in moisture or soil on that end.  That could be removed with a p-trap on the greywater landscape line, but I haven’t seen anyone put a p-trap on that side. Any thoughts?

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Hi,

You are right, if you’re installing a system in new construction you can use a standard vent. (Make sure to tie in to the house vents properly so there is no chance of a sewer backup causing sewage to enter the GW vent. ) Install a swing check valve before the vent connection to allow air in, but prevent greywater from getting pumped into the vent/drainage system of the house.

I don’t think you need to worry about any problems with the vent drawing in moisture or soil (the end of the greywater lines should not be sitting in soil, or water!). I would definitely not put a p-trap on the greywater side in an L2L system- it would just add friction, plus you’d need to increase the pipe size if you wanted to purchase a proper p-trap (they don’t make 1″ p-traps).

In new construction your whole system will be inspected, so the inspector may have requirements for the venting configuration of the L2L system.

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