  We critically examine the use of the Washington photometric system (with the
51 filter) for identifying distant halo giants. While this is the most powerful
photometric technique for isolating G and K giant stars, spectroscopic
follow-up of giant candidates is vital. There are two situations in which
interlopers outnumber genuine giants in the diagnostic M-51/M-T2 plot, and are
indistinguishable photometrically from the giants. (1) In deep surveys covering
tens of square degrees, very metal-poor halo dwarfs are a significant
contaminant. An example is our survey of the outer halo (Morrison et al. 2000,
Dohm-Palmer et al. 2000), where these metal-poor dwarfs dominate the number of
photometric giant candidates at magnitudes fainter than V = 18 and cannot be
isolated photometrically. (2) In deep surveys of smaller areas with low
photometric precision, most objects in the giant region of the color-color plot
are dwarfs whose photometric errors have moved them there. Color errors in M-51
and M-T2 need to be smaller than 0.03 mag to avoid this problem. An example of
a survey whose photometric errors place the giant identifications under
question is the survey for extra-tidal giants around the Carina dwarf
spheroidal of Majewski et al. (2000a). Accurate photometry and spectroscopic
follow-up of giant candidates are essential when using the Washington system to
identify the rare outer-halo giants.
