I had to make a custom tube for mine. I used stainless steel and a special bender and flaring tool from work, but you can use 1/2" (5/8" OD) soft copper water pipe. A cheap set of bending springs and a standard flaring tool is all you'll need. You will have to reuse the nuts as they are metric and not available as a flare-nut. Make sure you put the nuts on the tube BEFORE you flare the ends!!