Code:
unit Unit1;
interface
uses
   Windows, Messages, SysUtils, Classes,
   Graphics, ShellApi,Controls, Forms,
   Dialogs,StdCtrls, ExtCtrls;
type
   TForm1 = class(TForm)
     Button1: TButton;
     procedure Button1Click(Sender: TObject) ;
   end;

var Form1: TForm1;

  function SHEmptyRecycleBin
   (Wnd:HWnd; LPCTSTR:PChar;
   DWORD:Word):Integer; stdcall;

  const
  SHERB_NOCONFIRMATION = $00000001;
  SHERB_NOPROGRESSUI = $00000002;
  SHERB_NOSOUND = $00000004;

  implementation {$R *.DFM}

  function SHEmptyRecycleBin; external
   'SHELL32.DLL' name 'SHEmptyRecycleBinA';

  procedure TForm1.Button1Click(Sender: TObject) ;
  begin
   SHEmptyRecycleBin(self.handle,'',
     SHERB_NOCONFIRMATION) ;
  end;
end.