My sump pump is working fine, but during periods of little rain, I'm noticing a horrible odor in the pit. It is concrete lined, and there is about a 3" ring of scum between the pump trip line and the water level. There also appears to be scum on the top of the pump and some of the plumbing and electrical connections. Is this something I can clean out? What techniques/cleaners do you recommend? I've seen people recommend bleach, but that seams a little harsh to send into the storm sewer... Thanks!