To tell you the truth, it probably smells a little like the bottom of a well. It's indoors, under one of the bath rooms. The main problem is that it is a little too low to stand up right, so I'm feeling a bit like a monkey, one, because I stuffed the sump, and two, because I've just spent two hours draining and digging out the sand. Going to pop out and pick up the silicon and glass. Give my lower back a rest.