There is such a thing as PTFE (Teflon) tubing. It's not so unreasonably priced that one couldn't do this instead of using a straw. But I highly advise doing any burning/melting over an open flame outside. Probably better would be to use the clamps as the fusing source (get them hot enough to seal the ends for cutting).
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Experience is a hard teacher because she gives the test first, the lesson afterwards.