With our 12mth + trip coming up, Id considered a grey water tank a few times but never wortied about it.
Looking at a lot of free camps on the net it was stipulated you had to contain gray water so knocked one up today.
With no room under van now Ive added an extra tank, on the draw bar tucked in close to van was the only spot left. I used 150mm PVC pipe, with a tap one end to empty it. Will have to put buckets under drains on van the tip into tank but decided that was easiest. Will hold about 50lts.