I build this mobile shower to take with me on shore dive trips where no fresh water is available to rinse off gear. For the water tanks I used cat litter containers from Costco. Every 2-3 weeks I have one that normally goes into the trash, so this was a very cheap solution. I got the pump for $25 at Amazon, but you might get them at your local marine shop too. The car power connector is made from an old cell phone charger. I got all other pieces at the hardware store.
• 12V submersible pump
• Car power connector and cable
• One or more water tanks with a wide enough opening to get the pump in
• 1ft 1/2in hose
• ¾ end cap
• Shower hose
• ¾ in hose connector
• 2 hose clamps
I originally planned to build a switch into the power cord but found out that the way I use this does not require one, plugging the connector in and out the car power outlet worked just fine.