So several months ago I noticed some salt creep around a joint in the return plumbing system I have on the floor behind the tank, as well as up in the plumbing hanging down from the external overflow box, and I fixed it with replacement parts on the one location and a bunch of plumber's putty on the other (very hard to reach). So this evening, while squeezing into some other tight spaces to clean tank, I take the opportunity to a look at the one location and the other to make sure there's no more salt creep. Well, there's no more salt creep, but what the heck do I just quickly catch a glimpse of sitting on the bottom of the external overflow box (which fortunately is clear)? THIS!!! Given the amount of rust and other buildup on it, it's clearly been in there awhile..... Talk about catching a real break!