What type of tail piece to use when serving soda?

So i've been setting up my bar getting ready for football season and got some soda going. I went to drink it at first and it tasted fine, but a day later its got an off taste. So I check the lines everything was fine, and then I noticed the tail piece was rusted. I installed it about 2 years ago, and I have no idea what type of metal I used or where I got it from. Its a silver color so my guess is stainless or nickle, but I was under the impression those wouldnt rust.

you probably would have had the same problems with beer - brass or stainless would work great (stainless always has a narrow advantage). Plated fittings can give you trouble, since it doesn't take much to breach the plating somewhere, and then it's all over.