I have just moved house and want to install a dishwasher.The water and electric supply are existing and no problem to connect to.The problem is the waste water.I can just see and feel where the flexible pipe is connected under the sink area but can't get to it.Obviously the last owners couldn't either,and cut through their waste pipe,leaving a generous length behind.I bought a three quarter inch union,which pushes into the existing pipe with a nice tight fit,but is just too big for the waste pipe on my Bosch dishwasher(Because it's metric size pipe?) What would you suggest?

Remove what the previous owner had installed and start from scratch. Do you have a garbage disposer? Is Your Dishwasher Drain Installed Properly? - YouTube

No,don't have a garbage disposer.Starting from scratch means removal of the sink unit at the minimum,and possibly some surrounding cupboards.Money is tight having just moved house.I thought there must be an easier answer.

Bob is bang on when he advised you to tear out and repair the "cobble" job done by others, Your dishwasher drain will connect to either the disposal via a high loop air gap, (see image ) or through a branch tailpiece(see image) using a high loop and installing just under the kitchen sink drain. Good luck, Tom

What's the deal here pobbles? You ask a question, simply because you don't know the answer. You get an answer, actually 2 of them, and don't like it so you give me a bad rating mark. That's just not right now is it? I have never seen a kitchen sink where one could not reach the drain pipes, they are immediately under the sink so open the cabinet or post us a picture of what you got. Remove the cabinets, hog wash, post a picture and many of us could help you out.