This RSS trick isn’t much of a trick at all.

In fact it’s a function that’s built right into WordPress, but one that very few know of.

We’ve all come across a post that has a long (and I mean LONG) list of comments associated with it. Keeping track of these comments can be hard for the author, let alone the readers.

The Fix

This is why WordPress offers the following function to provide an RSS feed specifically for the comments of a particular post.

<?php post_comments_feed_link('» Comments RSS Feed'); ?>

Now there are 2 ways that you can implement this:

1. Place it inside your theme template in the appropriate location of your choice. (The code will generate the output, so there is no need for echo )
2. Place it inside a handler of a hook such as wp_list_comments_args. This will output the link right before where the comments our output using the wp_list_comments function. The handler should look something like this:

function my_wp_list_comments_args( $args ) {
post_comments_feed_link( '» Comments RSS Feed' );

// Don't forget to return the original arguments
return $args;
}
add_filter( 'wp_list_comments_args', 'my_wp_list_comments_args' );

How It Works

Calling this line of code will simply call the post_comments_feed_link() function that provides an RSS feed for the comments of a specific post, making it easier for your readers to keep track of those many, many comments.

Source: WP Recipes