We have a new-build house with an integrated dishwasher that was already fitted when we moved in. It's about 4 months old, and it recently stopped draining.
The engineer found that the waste pipe was clogged with fat. I was surprised, since I don't put fat-coated dishes in the dishwasher; although I do, sometimes, empty small amounts of still-liquid fat down the sink (naughty, I know - but it's not much, honest!). So the engineer pointed out that the dishwasher waste is plumbed in below the level of the exit pipe from the sink trap, so it will be sitting in the trapped sink waste-water, and any fat layer could enter and clog the dishwasher waste pipe.
I've attached a picture of the pipe arrangement below. My question is - is this a sensible arrangement for the waste pipes (and I'll just have to be more careful with fats), or is it a mistake to have fitted them like this (so I can get the builders to fix it)?