For kegs, I've just broken them down completely, given an extended PBW soak, then sanitize before storing, and then sanitize again, without issue. YMMV.
My plastic fermentors get an extended bleach bath with a high-strength bleach solution. The benefit of idophor and star-san is that they are no-rinse sanitizers, which makes them ideal for brewing. Bleach is not and must be rinsed, so there is the risk of re-introduction of microbes on rinsing. However, if you want to kill everything, bleach will do it.
I do mark my "soured" fermentors just in case, but right now my vienna lager is sitting in one.