Obviously sumps are some kind of pits. But where does the word come from and what else can we learn about them?
Well, first of all a sump can be a lot of other things than the ones I've mentioned. If you are looking up sump images, most of them will be metal or plastic as these days, we may first associate a sump with cars. In this case it's the oil reservoir in the internal combustion engine of a car. Sumps come in handy in mines, where water is accumulated at the bottom of a mine shaft. It can be a pond of water reserved for salt works. It can be just a pool or pond of dirty water. In fact, although I hadn't connected it before, we also have the sump pump, which removes unwanted water from basements. A sump, as far as I can tell, is a repository of unwanted or semi-unwanted things.
The Online Etymology Dictionary tells us that sump first came on the scene in the mid fifteenth century to mean a swamp or morass. It comes from the middle Dutch somp or the Middle Low German sump and goes back to the hypothesized ProtoIndoeuropean for "spongy". Our present meaning of "a pit to collect water" is from the 1650s. And that sump pump, first mentioned in 1884, was originally used in mines, not family basements.
The great slightly creepy photo is by Alfred T. Palmer. It was taken in 1927 and is entitled "OIL SUMP AT DRILLING RIG, SIGNAL HILL, LONG BEACH, CALIFORNIA". You can view a few more of his evocative images HERE.