Experiments were carried out in dusty plasmas of both the stratified and homogeneous positive columns (PCs) in a U-shaped discharge tube during its rotation from the vertical to the horizontal position. It is shown that in all cases the radial ambipolar field prevents charged dust particles from falling on the tube walls. For a vertically oriented tube, a dust cloud is observed only in a strong field of strata and is absent in a homogeneous plasma. In a horizontally oriented tube, the dust particles drift toward the anode in an axial external field. In this case, dust particles are trapped at the point of transition from the horizontal to the vertical section of the tube, in both the stratified and homogeneous PCs. It was concluded that for a V-shaped design of a cylindrical tube, an ambipolar dust trap, which is simple in technical execution, can be implemented, which makes it possible to hold dust particles in its lower part.