The only thing that comes to mind is a chemical toilet, and depending on where you are. You can get a camping shower from a basic plug into the cig lighter, up to full showers that run off the car heater
DISCLAIMER
All advice is given with-out seeing the job, and hence all advice MUST be taken as advice with limited knowledge on the exact situation. NO responsibility can or
will be taken. And yes, I am a licensed plumber with my own business in Brisbane Australia