Ever use a cast iron skillet?
It would take a lot more heat than anything lye could provide to make cast iron flinch.
said by leibold:
I compared crystal drano "professional strength" and insta-flo and while the active ingredient appears to be the same, the usage instructions differ between cold water (drano) and hot water (insta-flo).
When I bought the insta-flo the cashier at the hardware store warned me not to use hot water, only warm water.
For those that recommended insta-flo and have successfully used it, what water temperature did you use ?
In case it maters, my drain is cast iron (to the best of my knowledge the entire stretch from shower drain to city sewer).
I used near-boiling hot water right out of a kettle. Don't worry about the cast iron plumbing. I doubt the pipe even got noticlbly warm to the touch since they dissipate heat so quickly.