Nope. We have a cap with a garden hose connection to drain the grey when boondocking. We have been using a bucket when using public parks, but just ordered a blue boy since we are planning a 9 day trip to BC and using Provincial Parks.
If you have it capped off, there is enough room for a couple of quick hand washes, for anything more and it will backup--which you want to avoid because it can backfill into the black tank causing contamination of your grey water drainage lines and basins.
I do wish there was a grey tank. It is probably my only dislike of the systems on our 72 Overlander.