tarring a dump. Problems with a pipe

[vdemart1 at tin.it]

I'm getting accostumed to dump my fbsd 5.4 filesystems with "dump" on  
files in a samba share. Now, I'd like to compress the dumped files "in 
the making" (for instance piping it via tar) but I don't know how to do 
it.
Could you please help me?
Ciao
Vittorio