I have 32 Gal Blk, with 2 adults & 3 Kids (6,4,2) we can go ~5 days/4 nights.
Gray (32 Gal) on the other hand approx 2 days...we have a 25 gal blue tote so if the camp ground has a dump station we tote gray away daily. It takes about 10 min and means we don't have to worry to much about sink/shower water usage. If we go into full conservation mode, only min water usage. Basically for teeth brush, hand and face washing but no showers and dishes done outside in a tub we can make our gray last as long as our black.
2007 Chevy Duramax LMM/Allison
2012 Jay Flight 29QBH
2012 Jay Flight 26BH (Sold)