  We show that a combination of infrared photometry from WISE and 2MASS surveys
can yield highly pure samples of M giant stars. We take advantage of the new
WISE$\cap$2MASS M giant selection to trace the Sagittarius trailing tail behind
the Galactic disk in the direction of the anti-centre. The M giant candidates
selected via broad-band photometry are confirmed spectroscopically using
AAOmega on the AAT in 3 fields around the extremity of the Sgr trailing tail in
the Southern Galactic hemisphere. We demonstrate that at the Sgr longitude
$\tilde \Lambda_{\odot} = 204^{\circ}$, the line-of-sight velocity of the
trailing tail starts to deviate from the track of the Law & Majewski (2010)
model, confirming the prediction of Belokurov et al. (2014). This discovery
serves to substantiate the measurement of low differential orbital precession
of the Sgr stream which in turn may imply diminished dark matter content within
100 kpc.
