Hi,

Without seeing a picture I’m not sure how helpful I can be (and feel free to post a picture of the plumbing if you’d like).

Two ideas:

1. Backwater valves are required/needed when the drain is “subject to backflow.” If you are intercepting the water at a point higher than other drains there may not be a way for sewage to back up. For example, a vertical shower drain coming from a second story shower/bath would not be subject to backflow  if there was a fixture below it where sewage could/would back up and overflow out of before any sewage could back up into the greywater drain diversion. Hope this makes sense.
2. You could plumb a horizontal backwater valve along the side of the house before connecting back into the sewer drain. This may look a little odd, but it would be functional. You’d install the 3-way valve like an upside down T, on side would take greywater over and down to the landscape, the other side would connect to a backwater valve and then 90 down, 90 over, and connect back into the vertical sewer pipe.

Good luck with your project!

You have revolutionized my thinking! I’ve uploaded a photo with mock up of what I am now thinking based on suggestion 2. Due to the downspout on the left I am going to orient the T diverter (In red) to the right where it will deliver grey water (in grey). I will install a series of 90 degree turns (in green) with a horizontal backwater valve (in orange) before connecting back into the sewer line. Any suggestions on how much pipe should be used between 90 degree turns?

You have revolutionized my thinking! I’ve uploaded a photo with mock up of what I am now thinking based on suggestion 2. Due to the downspout on the left I am going to orient the T diverter (In red) to the right where it will deliver grey water (in grey). I will install a series of 90 degree turns (in green) with a horizontal backwater valve (in orange) before connecting back into the sewer line. Any suggestions on how much pipe should be used between 90 degree turns?