The risk of clogging drains is overstated, but they should not be used in septic systems. According to disposal maker Insinkerator, coffee grounds don't cause issues with disposals or drains, but can cause problems on unclean plumbing Insinkerator Blog. Coffee Grounds and Eggshells Once they're in your pipes, coffee grounds can collect over time to make particularly stubborn and pervasive clogging problems-especially if they catch other particles on their way down. The problem with coffee grounds has to do with what happens when they get wet. Remember: If it can fit down a drain, it can clog a drain. Here

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