I've recently fitted a kitchen. The furniture was budget but decent, and put together by a cretin at a local Travis Perkins shop.
I use "cretin" because he gave me a mismatched bath waste and trap, meaning that the trap wouldn't screw tightly to the waste. So I had to get another, which leaked, and then another, and now have a snug water-tight fit.
And I think he's done something similar when deciding on what basin I need - I think he's given me the wrong waste for the sink. THe sink is one of those with an integrated overflow (ie which is built into the porcelain).
He's given me a waste which appears to be the right one, but when it's tightened up, it leaks. Water appears to be coming from the union of the sink and the waste underneath, where the plastic bolt is which holds it in place. Before you ask, yes, I've put rubber washers on both sides, and after discovering the leak, I took it apart and put some silicon in to help too. No luck - it's still leaking.
Any ideas? I'm tempted to get a new waste and just start afresh, but I'm fed-up of wasting money.