one shot drain cleaner - de-rusting

[Bob Olive]

I'm with Parazine on this topic, the electrolytic system using washing soda is as safe (and as cheap) as it gets. One solution will last for ages, years even, with just top-ups of water and a quick scrape of the scum off the top. You can't overdo it, so you can leave it for hours, days or even weeks in very difficult cases, though I have never had to. Just try it...