I am looking for a very flexable tubing for uniflow in 4 oz plastic R/C tank.  I  want  something more flexable than today's average fuel line, even more flexable than the classic Prather fuel line (Yes, I understand there are two types of plastic tanks; the ones that are leaking & the ones that will leak)  The plastic tanks many years ago came with a VERY  flexable tubing that had to be changed at least yearly.  The clunk moved around very freely.  I am willing to change the tubing if needed.

The old clunk tanks used surgical tubing which is very flexible, but as you say needed to be replaced about once a year or so. I have not seen it advertised for years though.