  We study classical dynamics of an open string tachyon $T$ of unstable
D$p$-brane coupled to the gauge field $A_\mu$. In the vacuum with vanishing
potential, V=0, two fluid-like degrees of freedom, string fluid and tachyon
matter, survive the tachyon condensation. We offer general analysis of the
associated Hamiltonian dynamics in arbitrary background. The canonical field
equations are organized into two sets, fluid equations of motion augmented by
an integrability condition. We show that a large class of motionless and
degenerate family of classical solutions exist and represent arbitrary
transverse distribution of tachyon matter and flux lines. We further test their
stability by perturbing the fluid equation up to the second order.
  Second half of this note considers possibility of $V \neq 0$ in the dynamics.
We incorporate $V$ in the Hamiltonian equation of motion and consider
interaction between domain walls and string fluid. During initial phase of
tachyon condensation, topological defect at T=0 is shown to attract nearby and
parallel flux lines. The final state is fundamental strings absorbed and spread
in some singular D$(p-1)$ brane soliton. When string fluid is transverse to the
domain wall, the latter is known to turn into a smooth solution. We point out
that a minimal solution of this sort exists and saturates a BPS energy bound of
fundamental string ending on a D$(p-1)$ brane.
