pipe flushing

[Saville at micro.udel.edu]

Does any body know of any function to flush out
the write buffer at one end of a pipe?
and i don't want waht is flushed to go
through the pipe, i want is to be clean as if nothing were
to be written at all. or better yet, a function that
allows the write buffer to be removed(or not allocated at all).
and i'm using file descriptors......not FILE *fileptr.