I have dumped a couple that were badly infected in the course of fermentation. It takes only one such event to begin a regular schedule of extensive and very thorough cleaning (with the strongest agent you can justify), boiling (as able) and sanitizing with a highly effective sanitizer. I used to rinse well, sanitize with iodophor and call it good - no more. I change up regularly the approach and break things down fully a few times a year for a prolonged soak. But with the new plastics and their limitations, I find that I really have to treat each kind of vessel differently on the cleaning step (stainless - no more than an overnight soak in PBW; buckets - soak for a couple days in PBW; plastic better bottles - no PBW, but scrub well and use OxyClean for just a few minutes before rinsing and sanitizing). I am going to try Mark's suggestion about an ounce of TSP and an ounce of vinegar in five gallons of water for sanitizing, since he said it is not hardness affected. I haven't used One Step in years, but I may consider it for the quick clean and go approach that others don't provide....I have a bunch of samples from a judging this past summer.
Definitely a time to consider sanitation, again, BEFORE there is another batch to dump.