90 day service: why are things getting worse, not better?

So after we had some general fixing done a week or so ago, we ran the dishwasher and found our kitchen sink drainage with added extra leakiness.

As part of the 90 day service, the trades came and tested all the sink for drainage - but it looks like something got screwed up here, because out kitchen sink wasn't leaking before, and now it is.

Of course, I've tried tightening the drainage clamps around that U-bend, but it's still leaking. Don't know what the problem is, we didn't cause it, someone's gonna have to come fix it.

Still haven't heard back from Metricon about the few remaining items that need to be completed.

1. Repair and repaint cornice and plaster in garage from where garage door was fixed
2. Straighten/replace ensuite cavity door frame
3. Fix leaking kitchen sink

*edit* Went and checked the kitchen sink top to bottom - turns out they loosened the drain plug and forgot to tighten that one. So far so good.

T&T