Made this Camping/Beach shower after becoming violently ill seeing similar product prices at REI. You're welcome. Larger Capacity, Simpler Design, Won't Spill

Supplies

Chemical Sprayer - I advise writing "H2O ONLY" on it in many places. I never want even mild traces of chemicals in here. Why a chemical sprayer? because it has an integrated pump handle, very thick plastic, robust. I chose the 3 gal option.

Quick Connects - Nice thing about these is that they prevent spillage even when the system is under pressure. Buy 2 sets if you want to create an extension with the extra hose.

1/4" ID Hose - Make sure it is 1/4" ID (Interior Diameter) Tubing

Scrub Sponge with Hose - Love this thing. Such a nice way to shower and the water gets piped through the sponge! I have 2. and the plastic end tip with right into the 1/4 ID tubing for a tight enough fit. (you'll see)

(Optional) Schrader Valve - For lazy people who don't pump, thought I would use it more than I do. Actually I don't use it at all because the integrated pump is very strong and good.

(Optional) Electric Heater - Many Campsites have at least a plug in the bathroom. Heats up fast and heating element can just sit in there. I already had this so I take it with me now. Cheaper options available but make sure you do not get one that's not shielded so you don't melt the container.

(Optional) Jetboil - I had one of these already for cooking/coffee but here is the link in case you did not know this existed. Per my calculations, only 3 batches of boiling water can bring up the 3 gallons of water in the sprayer to a comfortable temp. In this case, make sure some cold water is already in the sprayer so that you don't melt the container.

Step 1: Cut the Sprayer Handle

Cut the black hose attached to the 3 gal sprayer. Cut it closer to the end with the integrated spray handle, but leave some room in case you want to use that as your shower attachment.

In my first version, I put a 180 degree bend in the stock sprayer and used that as my shower. Not your style? Fine one on Amazon. Many available. Or, use the sponge.

Attach the quick connect adapters, female side toward the tank. Attach the extension hose, length of your choice! Attach the spray Nozzle. Nice thing about these is that they prevent spillage even when the system is under a little pressure.

Attach the Schrader valve if you would like.

Step 2: Fill and Shower

I found that If I started the first day with hot water from my shower at home, it would still be acceptably warm that evening to shower after a hike, before bed. this also makes it easier to touch up the temperature if you were planning on using the jet boil.

With the sponge attachment, I also found that I was able to take pretty complete showers in about 1.5 gal which is impressive for my 6'2" stature. Yes, with soap too.

Release pressure when not in use so you don't blow a fitting and end up with water in your car. with that released, I retighten the pump handle and am not worried that, even in the sun, it's going to spill in the car.