I do not know what year yours is but this is the general how to. It did this so it would not freeze while we winter camp.
Under the sink in your case there should be a Tee in the hot and cold line. You just unscrew the feeder pipes to the outside shower. Then they sell and an inverted plug cap that screws on the Tee to cap it off.
I have bought then I think at Lowes. They are known as a 1/2" PEX cap if you have 1/2" pex tubing fittings.
Here is the Zurn brand. It was the only online pic I could find.
QuickPort Cap, 1/2" # QTC3FQPNPK1 by Zurn Pex
Hope this helps
Current Sunlines: 2004 T310SR, 2004 T1950, 2004 T2475, 2007 T2499, 2004 T317SR
Prior Sunlines: 2004 T2499 - Fern Blue
2005 Ford F350 Lariat, 6.8L V10 W/ 4.10 rear axle, CC, Short Bed, SRW. Reese HP trunnion bar hitch W/ HP DC
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