Nice photos and report.
Do you have more information on your shower set up?
I purchased everything at Ace Hardware: 2-gallon garden sprayer, flexible sink sprayer head/hose, hose barb connector, and hose clamp. Thread the brass connector into the flexible sprayer with some teflon tape, cut off the rigid plastic sprayer handle from the garden sprayer, and connect the flexible sink sprayer hose to it using the hose clamp. Fill the tank with water, pressurize it, and you're good to go. I've since painted the tank black and leave it out to warm up.
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