Clean or wipe move for delta 3D printers
Slic3r, and all other slicers that I saw, have an option called Skirt that enables your printer to print a number of lines around your object before it starts printing the object itself.

This should ensure that both the nozzle is filled with filament and the printer got rid of any burned / dirty filament when it starts printing your object.

If you use Slic3r as standalone, you have to activate expert mode in the preferences. If you use it through Repetier-host it should already be in expert mode.

You can see all available options in the Slic3r documentation for Skirt.