The best is steel pipe, the advantage is: not afraid of high temperature, not easy to leak. Disadvantages: the cost is a little high, and may rust after a long time.

The second is PUC pipe, benefits: low cost, not easy to leak. Disadvantages: long time use with high temperature drainage may be deformed, broken.

Now there is a kind of polypropylene on the market is the material pipe, this kind of is can be resistant to high temperature. It is a good choice!