The command line to empty Recycle Bin looks something like this :
ATTRIB %systemdrive%\RECYCLER\* -R -S -H /S /D
RD %systemdrive%\RECYCLER /S /Q
Put the above in a batch file, and that's it..
Sometimes RD won't do it's job, so to be safer side follow these :
ATTRIB %systemdrive%\RECYCLER\* -R -S -H /S /D
DEL %systemdrive%\RECYCLER\* /F /S /Q
RD %systemdrive%\RECYCLER /S /Q