Normally, to "kasher" or "kosherize" a metal sink (from non-kosher to kosher, or before Passover), you clean it out well, make sure it's used for nothing hot for 24 hours, then pour boiling water all over it.
At one point I got tired of shlepping kettles from stovetop to sink, and started thinking: what if I just filled the sink with water, and added in an immersion heater till the whole thing bubbled over?
Has anyone tried this? Is it halachically effective? safe? Practical?