If you plan on parking off-grid, or not connected to sewer, you will need a greywater tank for the wastewater from your sinks and showers. Greywater tanks come in all shapes and sizes. Use a portable one (on wheels) for easy dumping practices. I use this 15-gallon portable greywater tank. Anything larger would be too tall to fit under my trailer and too heavy for me to wheel around. I have to dump it once every day or every other day.