First - thank you all for the information you provide on here, it is incredibly helpful!

I'm fixing up a small 40's house (900 sf) and overhauling the plumbing. Half of the house is over a crawlspace, the other on a slab. The house is on a small septic tank and has city water.

I have removed all of the old supply lines (1/2" PVC spliced all over) and while working on moving the washing machine drain noticed that the washing machine, shower, and kitchen sink drain are all connected to a 2" pipe that discharges to the storm ditch by the road.

Two questions about this. One - In the code (2012 NC version found on Google) it mentions that greywater can be discharged into an approved trench which I'm assuming this would be. Is this legal? How would I find out if the trench is approved?

Second question is if this is legal, are there any requirements as far as treating or filtering the greywater before it is discharged? I would love to maintain this setup to minimized the load on the septic system.

As for the washing machine drain... I would like to move the laundry room to the portion of the house that is on the slab. In order to do this, I'll have to run the washer drain through a non-load bearing stud wall, through 3-4 studs. The OD of 2" pvc is 2.375" which means the bore would have to be 2.5", leaving .5" on either side of the stud.

To further complicate things, there is a row of 8" block between the slab (Finished floor) and the plate of the stud wall. So I guess my question is.. Is there a reasonable way to route the drain from the washer box through the wall? This will have to pass inspection.

Thanks in advance for your help!

The washing machine drain has to be 3" here in NC as soon as it turns horizontal, you can only use 2" on the vertical.
As far as the grey water it is a code violation as is , and you will be required to bring it up to code if any inspectors are involved in your project. The county health department may issue you a variance on the gray water. They will need to come out and inspect the current sewer system, observe any future repair area, property lines, soil type, etc. If they issue a variance, you will need a backhoe to dig a hole and a dump truck to fill it with wash stone gravel. The health dept. will give you the dimensions of the hole and amount of gravel required.

"The washing machine drain has to be 3" here in NC as soon as it turns horizontal"

I've never heard/read anything like this. You're suggesting 2" standpipe/trap and then an increase to 3" directly after the trap?

If your trap is teeing into vertical vent, you must go to 3" pipe at the base of the stack, as soon as the drain turns horizontal. If you are taking your vent off the horizontal drain , you must go to 3" as soon as you get to the vent. So you will have to use a long sweep 3" 90 with a 3" X 2" bushing in the top, or a 3" X 2" wye with a 3" X 2" bushing in the back of wye.
It's under UPC with NC amendments, it has been code since about 2010.

First not from NC, out of California<
The last time I look at this there is a section for simple greywater system.
In this case the code is looking for you to dump the greywater into a mulch trench to feed your plants and trees. You can extend the 2 inch pipe into your garden area and have branches that go in different direction to feed different part of your yard. At each tree use 5" landscape cans buried in mulch to discharge the greywater. The key is that all greywater is should never be place on the surface, where human contact can occur.

There should be an option to direct the greywater to the septic tank, just encase your need to wash the bathroom with harsh chemicals or a toddler who pop in the tub.

For the laundry, i would suggest using a 3/4 pvc pipe from the laundry hose to the drain nearest drain pipe. Check with your inspector, but it is just like running a SanFlow sump pump for a washer in the basement. Where the washing machine in too low for the sewer system. You will need a air gap and check valve to prevent the laundry greywater from backing up into the washing machine.

Take the opportunity for reuse the greywater from both sources on your landscape. Greywater can be used to grow fruit trees, vegetables and grass lawns.