Dregs is a noun that refers to the remnants of a liquid left in a container. 

The origin of our word of the day is unclear, but it seems to have emerged from Scandinavian, then later found its way into Middle English. Dregs may refer to the remnants of a liquid or an undesirable part of society. Either way, it is almost always used in the plural. 

I’ve been trying to clean my thermos for a while and for some reason, I just can’t get those dregs off of it. The remnants of all that orange juice can get really gummed in there.