How to uncover "Shared" OBL in "Related: Search"

[girish]

Background-
Google's "related:www.domain.tld" command returns up to 30 sites G considers to be "on-theme" with the target site. The results from the "related:" command seem to be based on linkage. It shows other pages/sites with backlinks from the same sources. In other words-- If page A links to page B and page A also links to page C, then if you check related:siteB you will find siteC listed and, vice versa, checking related:siteC you find a siteB.

(There is tool at [touchgraph.com...] which graphs a site's the related: search results. [webmasterworld.com...]

Here's my question-- When I do a related:search for SiteB the #2 result (out of 30) is SiteC which apparently is not at all related. SiteB is about Auto Insurance, SiteC is about Stereo systems. Similarly, a search for related:SiteC shows SiteB as the #3 result. All other results for both sites are related to each theme. How do I uncover the "common" Page/Site A that must be common to B and when none of the related:results that show up for B and C are common (other than these two sites themselves)?

I tried using the link:domain command and was unable to find the mysterious "A" site that way. Any suggestions?