title_body: Will emptying used coffee grounds into the sink drain damage my pipes?
upvoted_answer: You don‘t need the advice of coffee drinkers, you need advice from a plumber (which I am admittedly not, but I have enough contacts in the industry) and a gardener to chime in.
  
  In short: Don’t do it.  
  
  Coffee grounds may smell nice and there is that persistent old wives’ tale that will claim that it has [some random positive effect]. It’s not true. Any plumber will tell you that it’s best to pour nothing except liquids down the drains. Coffee grounds are particles that may
  
  
  clump together 
  collect like sediment in traps
  bind to other fatty residue
  provide food to microorganisms that form that slimy and stinky biofilm in the pipes.
  
  
  And yes, most plumbers will love you for the habit of washing down your grounds, because it keeps them in business. 
  
  Coffee grounds are lovely additions for compost, so either simply add them to your garden compost or treat them like you would any other plant-based kitchen waste.