My '07 Ragen has 58 gal black and 58 gal grey. My original literature said the lavatory sink drained into the black tank, but I did a simple test with a 5 gal bucket of water and discovered this was not true. It didn't take me long to figure out that the black tank was only being used to a fraction of it's capacity, so I plumbed a crossover pipe between the 2 tanks. Now when the grey tank gets full it starts running over into the black tank.
Two of us can go a good 3-day weekend washing dishes and showering with no issues.
