  We solve the feedback stabilization problem for a tank, with friction,
containing a liquid modeled by the viscous Saint-Venant system of Partial
Differential Equations. A spill-free exponential stabilization is achieved,
with robustness to the wall friction forces. A Control Lyapunov Functional
(CLF) methodology with two different Lyapunov functionals is employed. These
functionals determine specific parameterized sets which approximate the state
space. The feedback law is designed based only on one of the two functionals
(which is the CLF) while the other functional is used for the derivation of
estimates of the sup-norm of the velocity. The feedback law does not require
the knowledge of the exact relation of the friction coefficient. Two main
results are provided: the first deals with the special case of a
velocity-independent friction coefficient, while the second deals with the
general case. The obtained results are new even in the frictionless case.
