Plumbing and water heaters
How to troubleshoot and a fix a clogged sink drain - learn easy DIY plumbing repairs
...sink starts to fill up immediately then you know the blockage is beyond the P-Trap and you need to work further down the line to solve the problem. At this point, try a drain solution, and we would advocate using an organic one first.
If a drain clearing solution doesn't work then the next step is in the basement. Hope...