Four Wheel Campers like mine that have factory sinks drain to a garden hose fitting on the side of the camper. There is no provision for waste water collection and later disposal in their design.
When I built out my camper shell (no sink or drain) I decided to address this issue of wastewater. I park in parking lots, paved campgrounds, gravel and dirt.
My decision was to be able to drain to the ground or collect my wastewater. Above is my salad bowl sink I made that comes down to a garden hose wye with shut offs.
The wye feeds 1/2” tubing with one tube through the void space between the camper and interior truckbed wall. The tube goes down through an original hole in the Tacoma poly bed. I let waste water go down this hose when disposal on the ground is appropriate.
The other tubing goes to the 4 gallon waste water tank that I can remove and dispose of later. This works well for stays in parking lots and paved campgrounds.
I use a quick garden hose disconnect on the tubing going to the tank. Above is my collapsing pail with the tubing to the tank collecting waste water in the pail. I show this as doing this puts the pail in the way of the sink front and makes it easy to knock over. I could place the pail under the truck beneath the hose that drainscto the ground but a plastic pail is light and the wind can and will blow it around.
It is possible to use a basin to wash dishes and then to carry the basin to toss out the waste water.
They key is to respect the environment and leave no trace. I have switched to Camp Suds to make my waste water more environmentally friendly.
The key to your waste water is be restful where you stay. Even when I was in my Prius I had a wastewater tank that I would dump. The ability to select to store or send to the ground simplifies how I dispose of my wastewater.