  We present a detailed analysis of the behaviour of the Red Clump K-band
absolute magnitude (M(K,RC)) in simple and composite stellar populations, in
light of its use as standard candle for distance determinations. The advantage
of using M(K,RC), following recent empirical calibrations of its value for the
solar neighbourhood, arises from its very low sensitivity to the extinction by
interstellar dust. We provide data and equations which allow the determination
of the K-band population correction Delta(M(K,RC)) (difference between the Red
Clump brightness in the solar neighbourhood and in the population under
scrutiny) for any generic stellar population. These data complement the results
presented in Girardi & Salaris(2001) for the V- and I-band. We show how data
from galactic open clusters consistently support our predicted Delta(M(V,RC)),
Delta(M(I,RC)) and Delta(M(K,RC)) values.
  Multiband VIK population corrections for various galaxy systems are provided.
They can be used in conjunction with the method devised by Alves et al.(2002),
in order to derive simultaneously reddening and distance from the use of VIK
observations of Red Clump stars. We have positively tested this technique on
the Galactic globular cluster 47Tuc, for which both an empirical parallax-based
main sequence fitting distance and reddening estimates exist. We have also
studied the case of using only V and I photometry, recovering consistent
results for both reddening and distance. Application of this method to an
OGLE-II field, and the results by Alves et al.(2002), confirm a LMC distance
modulus of about 18.50, in agreement with the HST extragalactic distance scale
zero-point. (abridged)
