Bathroom sink slow water

[Alanaver]

Need help. Bathroom sink water drains very slowly, have tried changing waste to a trap but this has made no difference and you can always see water in plug. When I took the waste apart to fit the trap, I poured water down waste pipe and it appeared fine. Have no other issues with waste slow draining in house. Would appreciate any thoughts on best way forward without needing to call out plumber.

[Elmebrigge]

I also faced this problem a year ago, and I am not sure about the solution.
Actually, I called some plumber and he told me about the origin of water pressure.
Then he did something and I felt relaxed.