Ahhhhh, this subject again. Yep, right up there with traveling with propane on, and all the other subjects that RV folks will debate until the end of time. :)
I use a 25 gallon 4 wheel Barker tote tank for just this purpose. I just empty the RV's grey tank into the Barker tote tank, roll it over to car, tow it to dump station and dump away at dump station. Pretty simple and easy.
But I DO have to confess: Sometimes, when we're in more remote, rustic parks where there's nobody camping close by us, and I really don't feel like messing with the blue tote tank.....I *might* just 'accidentally' open the grey valve just a little bit, let it drip, sloooowly drain out on the ground. If you do a slow drain like that, most times there will be little or no stink, as ground will absorb it almost as fast as it drains out.
Ironically, using the tote tank can sometimes create more 'stink' than slow draining the grey water on the ground. WHy? When you dump your grey water down into the tote tank from the RV, you have to open an air vent on the tote tank to allow air in the tank to escape as water fills it. Guess what that air coming out smells like? It usually creates more grey water 'stink' than slow draining like I mentioned before. This is also why I try very hard to avoid using the tote tank for black water, the air coming out then can be REALLY bad, haha. :)