This may depend on floor plan as I do not think it would of worked on our prior T2499. I dealt with that camper differently on this topic.
On our T310SR, I did "unhook" the outside shower as we winter camp with the fresh water system fully active. (we have enclosed heated tanks) The outside shower being pressurized was a potential risk to freeze while we where camping. I use to insulated the outside compartment, but later stopped doing that and just unhooked the water lines feeding it inside and capped off the Tees. And have not used it since. Now 5 plus years ago.
This was easily doable the way our plumbing was made due to the floor plan. If I ever wanted to come back and use the outside shower in the summer months, then I would hook up the pig tail feed lines from the tee to the back of the outside faucet.
I "think" I have some pics of this, I will post if I can find them or I'll go take some more as it is unhooked right now.
Again, in my case I just needed a pex cap that would screw right on the Tee to seal off the outside shower and I removed the supply feed tubes off the back of the faucet. My tie in tee's are pointing up so when capped off and the main line drained, no water remains in the Tee. This all happened in the cabinet under the bathroom sink as the outside shower was directly outside. The feed tubes were only about ~ 12 to 16" long.
Do you know how your outside faucet is plumbed? Can you get to the tie in tee's? Where does the outside faucet supply tube tie into the main water lines and can you get to that area?
What I was able to do, may or may not work on your floor plan, and piping setup, but it might.
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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