Back pressure when draining sink.

[aks060476]

I recently had a new kitchen installed. I have a connection under the sink for a dishwasher but don't have one. I have 2 sinks, the main sink and a small drainer. If I attempt to drain both sinks at once the small blue stopper that is blocking off the spare connection for a dishwasher blows out and water goes everywhere. This also occasionaly happens when I use the washing machine.

[rosebery]

Poorly plumbed waste. Get the fitters back to fix it at their cost.

Cheers