How to use command on output of processed tail -f?

Question

So I monitor some logs (/var/log/apache2/error.log) with the command tail -f, and only print the errors (grep ':error'). I combined both of these in a script (namely, watch_error_log.)

NB: I am part of the adm group.

So far so good.

But when I attempt more useful tricks, it won't work, such as :

$ while read APACHE_DEBUG_LOG; do echo "$APACHE_DEBUG_LOG"; done < <(watch_error_log)
or
$ watch_error_log | while read DEBUG_LOG_APACHE; do echo "$DEBUG_LOG_APACHE"; done;

Of course, my goal is not to ECHO the output. But If echo won't work, I know it is not because of the other program I want to use.

Why doesn't it work, and how can I make this work ?

After reading piped command after grep not working, I tried to add --line-buffered and everything's good.