[ghorrocks]

Make sur eyou understand what the categories are:

Continue from last time step : These are the number of particles in the flow and carrying over from the previous time step.

Left domain : These are the particle which exitted the domain, probably via the outlet.

Collected on walls : Obvious

Waiting for next time step : These particles are still in the domain at the end of the time step, so they will become "Continue from last time step" in the next time step.

Also note that if your domain is 1m long, with a velocity of 1m/s and 1E-6s time steps it will take 1000000 time steps for a particle to get from the inlet to outlet. This is no doubt what is happening in your case - you just need to wait longer.

The dancing as it exits the infill (which is clearly visible) means there might be dancing inside the infill which you cannot see. The stuff inside the infill might be important for particle deposition.

Definitely look at Eularian particle tracking. In many cases it is faster and more accurate than Lagrangian.