This is a screw, that screws on the bottom of the standard bathroom drain cap. STL and ZIP (OBJ) files attached.
60-100% to make it strong
You could set some setting that will help in printing the srew overhangs, or use support.
I recomned printing it from a hard, (chemical, and) heat resistent materia, PLA and ABS is good enough.
The Epic Bathroom Sink Plug
+Top of the plug
+The side of the plug, and nut
Assabled (screw it together)