Slow Draining Bathroom Sink

Hi all.

I'm having a bit of a problem with my bathroom sink. Basically it is very slow draining, and takes up to a minute to drain a few centimetres of water. Obviously I assumed there was a blockage so used drain cleaner and a snake to try and clean it. This didn't work so I removed the p-trap and cleaned it out, but there was nothing significant in there.

I held the sink bowl over the bath (with p-trap attached) and used the shower to put water in the bowl and it it drained freely. I poured water into the waste pipe and it didn't block either. However when I attached the sink back to the waste pipe it still drains very slowly.

Does anyone have any ideas what could be causing it to drain so slowly?

Thanks in advance.

Mike

 

Have you a pop-up waste, it may need adjusting?

 

No, it's a rotating plug similar to the one in the link:

http://www.homebase.co.uk/en/homebaseuk/flip-basin-slotted-basin-waste---chrome-941670

We used to have a pop-up plug (one where you press it to release it) but the hard water and slow draining caused that to seize up so I replaced it with the rotating one.

 

You probably have a restricted pipe further down in the run, time to investigate.