see these posts.. it seems that piping "tail -f" works with some OSes and does not work with some...
http://www.computing.net/solaris/www...orum/1734.html
http://www.zsh.org/mla/users/1999/msg00360.html
you did not tell whether...
tail -f log_X | grep n
worked on your system.. i.e., you can see the stuff on your terminal..
Cheers!
Vishnu.