let's backflush the hot backwards from the showerhead to the hot water
tank. run hot and cold water thru showerhead, tub spigot, showerhead,
remove showerhead and clean it and set it aside. cap the shower arm
with a 1/2" female threaded cap.
turn on shower cold.
back at hot water tank turn off cold supply to it.
connect drain hose from bottom drain to a sink or floor drain and open
let the cold water backflush the hot supply line all the way to the hot
tank drain hose 5 minutes or longer until its water drains clear when
viewed in a white plastic bucket.