Graywater overflow plumbing… which design to choose?
1 is better (so long as that valve has essentially no restriction). Otherwise you might need some height above the valve to keep the flow happy.

In version 2, turn the tee on the greywater line around so it goes where the overflow would go, and put in a trap (currently it allows sewer gas to vent into the greywater plumbing.) In fact, if the valve does what I expect, it forces septic venting into the greywater plumbing. So, not good.