I just had to go change my tshirt lol.
Thought what happenes if I put my thumb over the end of the connection where the water from the shower head comes into it and see if it’s forced out the other end. It just comes out the shower head and soaks you 
and then the back pressure pushes the water back out when I take my thumb off.
I am going to leave it as it’s worked for the 12 years we have been here , just not as well as I would like compared to the others here.
lol, gotta empty the line between shower and valve first, forgot to mention that. I always turn my valve to halfway, which drains water from shower head down to valve (clears everything on the demand side of the valve). Was taught to do that here as many houses in my neighborhood had crap insulation (originally summer homes) and the plumbing is on an outside wall / didnt want standing water to possibly freeze in winter. (not sure why we werent concerned with the pressurized lines feeding the valve, but I was a kid and didn’t think about that then).
Personally, I would just unscrew the caps and remove both of the white lines from the brass T. Blow in one side, if air (or water) is forced from the other, you know its a loop. And honestly, a loop between valve and showerhead, or a T that goes anywhere for that matter, is pointless as the shower needs to be on to send water to it. If its a loop, I would just replace the PEX line from the valve to the showerhead, and cut out the confusing and extraneous plumbing while you have the wall exposed.
OK I will disconnect the other side and play a tune and see what happens lol.
Then terminate the ends off and wait and see if anything changes before putting up the drywall, guaranteed if I don’t test it fully I will have to take the drywall back off and re connect it lol.
that sounds like a good plan…
At the other end of those white lines, is there anything at all that could use water. It seems like an awfully long run to fix a mistake, ya know?
But, based on water dynamics and principles of flow, the loop wouldn’t return water (act like a loop) as it has only one input at the T. Any water that goes out the T on the line between valve and showerhead, would just fill that line and stay put eventually, unless there’s a valve / exit somewhere on the other end.
And again, why would it be tied into the shower having to be ON to work? And 1/4" lines aren’t enough for another shower, or even a faucet really…
On the far ends of the white lines, outdoor shower? slop sink? you already covered humidifier in furnace.
Exactly, there has to be a device using the water or hookups or something- not a loop.
Not gonna lie, was looking forward to your update all night.
I don’t know where they go or end up.
I hate mysteries, my personality makes me slightly obsessive trying to understand and work them out lol. It’s not practical to rip the floors up to find out but it’s driving me crazy now.
Going to get my airbrush compressor up here and put some air with a bit of force in the pipe. I think our water pressure is around 50psi so 30psi of air should be safe I hope lol.
The mystery deepens. I just remembered they had a washing machine up stairs in a wardrobe, in what would be a spare bedroom. It was too noisy so I moved and plumed it into the basement. I just jammed my head up between the ceiling joists and can see the pipes go back up through the floor where that washing machine was originally. That washing machine had 1/2 in pex pipe with on off valves so I just turned them off and put a patch of drywall over the hole in the wall. Then capped the drain pipe in the floor and laid a harwood floor over that.
If you look at this logically it doesn’t make sense to have a washing machine water feed that needs the shower to be running to access water though. If it’s not a closed loop then water has to run somewhere, and why would you want to waste your water when showering. Why would you have a closed loop attached to a shower…
Aaarrrgghh!!!
I don’t think it’s logical- I think whoever plumbed it didn’t know what the fuck they were doing, probably thought they were getting cold water (hence the blue PEX?).
I know well how it is to be obsessed. Now that you know where it goes, that seems enough, no? You know you can disconnect it and just ignore it.
I think you are right, the evidence suggests they didn’t know what they were doing plumbing in the other shower valve backwards.
I am just going to terminate all three ends and leave it at that. Wasted too much time and energy already, and running behind schedule for my other outside stuff, I need to do while the sun is still shining.
I’m betting… They wanted to add water line to run to washer. But didn’t know how to read the plumbing, and put it in the wrong place. Water takes the path of least resistance, between the head pressure, and pipe reduction pressure, unless you could also turn the shower head off while running the shower, it would not push much to the floor above…
Oh the joys of home ownership!!!
With many shower valves you can just flip the cartridge instead of replumbing the supplies correctly.
Yeath thats what I am hoping lol.
After sitting there looking at it, I think that’s exactly right. Some idiot T’d of the wrong pipe to take water somewhere, and when they realized what they did, got the supply from the other bathroom probably and just connected the ends together. when I blow in one end I cant feel any air pressure but I here gurgling noises from the other end that stop when I stop blowing down it. 
Hmm… The gurgling deepens the mystery. I expected you to blow air/water out, or to not be able to blow at all… Gurgling could just be the way the hose is sitting / belly, and air getting past essentially a j-trap in the 1/4" line. To feel pressure, you might need an air compressor instead of your lungs if theres some water trapped (gurgling sound). That water would diffuse the flow on the other end and you’d barely feel it with lung capacity / force.
Just had a buddy come around and showed him the plumbing. He said he saw a similar set up where he works. He said the reason for the one at work is to to stop the water traps drying out and allowing the septic tank gasses coming back up into the building if it gets unused for a long period.
It makes sense as the other bathroom shower rarely gets used, it could be one line to the shower and one to the washing machine, that’s been moved. The crushe’d copper pipe stops too much pressure and water being lost to the shower head.
I guess I should connect it back up, I knew as soon as I cut it, the probable reason would be found lol.
OK, even if that’s really the reason for doing it I don’t think it’s viable.A trap holds a finite amount of water no matter how much piping is attached to it. So the theory of that piping, being used to keep a trap full doesn’t work. The trap will only fill so much, the balance drains away. So in a rarely used shower, there will be no difference in how long it takes for the trap to dry out, with or without that piping.
If that trap drying out is a valid concern, throwing a quart of water in every once in while would work.
and when the trap drys…the sewer gas will come out in the shower head. I would keep that loop closed just in case any one tapped it into a waste line/trap, and replace the riser pipe
This piping comes from the shower that gets used every day, and I believe it goes to the other shower that gets used maybe twice a year if that.
I don’t know for sure where it goes, but as we have never had any bad smells from the bathroom not used much it seems plausible.
I just don’t want to rip a new shower out a couple of weeks after putting it in lol.
When us women entered the skilled trades plant, they converted a bath and took out the uranyl. Big mistake. The trap dried out and the smell entered the room. We kept the drain covered with duct tape and added water to the shower that was being used for storage. After we drenched everything in the shower a few times they moved the stuff elsewhere.
I wish they had done something like that.
If it is that, then I wish that they took it from the kitchen sink instead where your water pressure is not really a concern, where as low pressure in a shower is very annoying lol.
Agreed!
