Recycled Water Irrigation recommends that all new houses should have accessible grey water pipe outlets or simple diverters installed.
The technology in grey water reuse, treatment and diversion is being developed all the time. Once these pipes get locked up in a concrete slab and/or mixed with black water, they are unable to be used for the life of the house. This could be as long as 40 years or more, wasting potentially five million litres of grey water that could have been re-used for irrigation, or retreated for car washing, laundry and toilet cisterns.
There are some cheap simple diversion devices on the market. But even a DWV tee junction with a ball valve is all that is needed.