shower supply question

[MarkMark]

just wondering on my shower supply line there is a 1/4 flexable copper tube tee'd into the supply line a few feet before the shower head. just wondering what this is and where it goes too?

 

[MarkMark]

i followed this tube and it is delivering water whenever the shower is on to a drain in the basement, this appears to be just a waste of water (esecially hot water) has anyone heard of this before and is it nesesarry?

 

[Sponsor]

 

[Cass]

It sounds like some DIYers idea of keeping the trap from drying out and causing sewer gas to finds its way into the house.
I would eliminate it and use RV antifreeze in the trap to prevent it from drying out.