Plumbing - Drain Primer Sink Takeoff
It works best to use the 1-1/2" version. On the end of the 1-1/4" sink drain pipe (that typically has the plug popup mechanism) you fit a 1-1/2" take-off assembly. This connects to the sink drain pipe using an ABS male screw piece and an ABS 1-1/4 slip ring piece.
There is also a 1-1/4" version but using it requires an upside-down slip ring joint which is likely to be unreliable.
1-1/4" version that has a fine screw thread top is http://www.homedepot.com/p/Keeney-Manufacturing-Company-1-1-4-in-x-8-in-Brass-Chrome-Plated-Threaded-Trap-Primer-56SN/204373995?quantity=1