If the smell coming from your sump pump reminds you of rotten eggs, and there’s water inside the pit, sewage may have entered your sump pit. Since your sump pump collects water under your property’s foundation, a sewer line may have broken, causing the sewage and your foundation water to merge. There should always be some still water in your sump pit. That water protects your basement or crawl space against underground gases and sewage from going up. When there isn’t any water in the pit, and it’s dry, those underground gases enter your basement causing a rotten egg smell.