Red PEX, so it has to be hot water piping. My guess is a shutoff for hot water to the outside shower above it on the outside wall. That is the only hot water in that area.
I can tell it is a GT like mine, but it is good to specify GT or Lounge.
...; and I was wondering whether that piper is Scottish.
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John W. Irwin
2018 Interstate GT, "Sabre-Dog V"
WBCCI #9632
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