When I had a dishwasher installed, the plumber refused to install the waste water pipe horizontally, saying that this would get it to clog all the time. He left a roughly 1:10 slope on it. I thought it made sense.
Now I find that the drain pipes that my sink and bath are connected to (and which clog up all the time) are lying on the floor completely horizontally, for a length of at least 1.5 meters. They are 4cm diameter PVC pipes.
Is this a bad installation, and do you think this is why it keeps clogging up? Are there legal requirements in the UK for the drain pipes to be sloped, so I could get my landlord to fix these?