How do these two pipes under my sink connect?

Mutton_Geoff

Did both bowls drain slowly before? If so, the restriction will be in a common part of the pipe, ie the main outlet to the drains.

To get rid of fat deposits, fill both bowls with water as hot as you can get (add kettles of boiling water) and a good dose of washing up liquid. Then pull both plugs out one after another and let the flow of very hot soapy water wash the fat away.

I always wipe fatty pans with kitchen towel before washing as the fat will be soluble in the hot dishwater but solidify when the water cools on it’s way to the drains.

If your outside (larger) drains are accessible and you have a jet wash, I highly recommend the drain cleaning hose attachment you can buy. It acts like a rocket powered snake and scuttles off down the drainpipe cleaning as it goes, but it’s not suitable for the first part of your drain from sink to gulley.