Your shower water goes to the gray tank...... In the pic of outside shower, pull that white flexible hose out. It is hose that connects to shower head. Pex plumbing inside camper goes to the taps. If you turn taps on the way it is, you will be running water somewhere inside camper from that white hose. Over the years I have taken those shower heads off my 3 different Bigfoot's and adapted a sink sprayer hose & head. Much easier to use and conserve water dry camping. A threaded white plastic fitting from hardware store has same thread as shower hose, and then a brass reducer bushing into that to adapt to sink sprayer hose.
If your inside taps base for shower hose is cracked and needs to be replaced, it is a big job. I did it on my 2002 2500 9.6. I had to remove both outside shower box and city water hookup box so I could get arms & hands up behind sink from outside, then work by feel only to undo Pex waterpipe fittings and plastic spud nuts from taps so taps could be removed from inside, then reverse proceedure to install new taps and reconnect Pex water pipes. After putting plumbing boxes back into fiberglass shell I resealed around them with Geocel.
I have two of those showerheads & hoses sitting in my garage never used. I think they are pretty common equipment, probably find them in an RV store.

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