The flexible PVC fitting (which was leaking) is gone, replaced by a regular PVC tailpiece. All the less than professional pieces of teflon were also removed. Again, that was a hack job done by a poorly informed homeowner: teflon tape lubricate threads, it is not a mean by which one can plug a leak.
The popup drain (which was leaking – see the redish, rust like traces on the grey tailpiece) was unassembled, cleaned and re-installed with new gaskets. The popup drain screw was tightened by hand ; just enough to prevent leaks. This is another mistake made by too many: you should only hand tighten SLIP Joints first and slowly tighten them 1/4 of turn at a time to plug leaks.
The 90 degrees ABS P-Trap adapter solvent welded on the drain was replaced with a solvent welded ABS HUB x SLIP fitting which allows transition from ABS to PVC.
This project was easy but took a long time because there was not much space under the vanity. It was not possible to take the vanity out so I had to unassemble the drawers rails to get some space to work!