All of the above suggestions and... We found a plastic tub that fits perfectly in the kitchen sink. We just dump the tub in the toilet when finished dishes. Black tank rarely gets full.
If you are planning on dumping your grey water on the ground (only do so when you are sure it is allowed and you will not offend anyone) try this. Get a sewer cap with the garden hose fitting. Take a plastic kitchen scrubber (the green rectangular ones, about 1/2 inch thick work well) and cut it to fit inside the cap. I stuck a piece of velcro on the inside of the cap to hold it in place. The pad acts as a filter and removes all food particles and much of the soapy suds, the two things that I find rather disgusting when I pull into a campsite where somebody has dumped their grey water. Use a length of garden hose to direct the grey water to an inconspicuous spot, like under a shrub. When the pad filter gets grungy, toss and replace.
