A few years back, my wife and I toured the Brightwater sewage treatment plant in south Snohomish county, to see our $ 100/month sewer bill in action. The tour guide made a big point about flushing wet wipes down the toilet and dumping oil/liquid grease into the sink was the bane of their existence, and they had elaborate traps to try and separate this out from the waste stream before it started the biological/chemical sewage treatment.