We've all been there ... the grey tank always fills up before the black tank ... which makes sense. All used water except that for flushing the toilet goes into the grey tank. (There are a few models where the vanity sink drains into the black tank, bu the way.)
Water conservation when camping without sewer hookups is a must, but it's not that difficult to do: navy showers, using paper plates, using a dish pan to wash dishes, rinsing clean dishes efficiently, putting the used dish water down the toilet (sans silverware, of course!), cooking on a grill outside to cut down on pots and pans ... all ways to extend the time between grey tank dumps ...
We use a dish pan for dish washing, so we wipe down dirty dishes with a paper towel (which also helps minimize "gunk" in the grey tank) and "store" them in the dish pan until we have enough to wash ... that way we aren't washing dishes every time we have a meal, so we wash dishes only once a day, if that.
While allowed in fewer and fewer places, in some locations it is OK to drain grey water onto the ground ... but you should check before doing it ... Some parks clearly forbid it ... if that's not the case, you can ask a park volunteer or ranger if it's allowed.
TB & Greg and Abbey Schnauzer
AirForums #21900 . Membership Chair, 4CUnit #3954
Travel Log: AZBambi...On the Road Again