Third-Level Push (aka “siloing”), according to Dan Thies (who regained my attention after his recent article on Google proxy hacking), helps you get third-tier pages (e.g. article/product detail pages) in the main index and ranking higher by “taking more of the PageRank from your second tier, and pushing it down into the third tier.”
Dan explains:

In most sites, your global navigation links to the entire second tier from every page, including the home page. This causes the second tier pages to accumulate a lot of PageRank, at the expense of your third tier.

Makes perfect sense. Most sites with moderate PageRank (home page TBPR 3-4) often have no problems getting the home page and most of the category pages in the main index, but they often can’t get some of the product detail pages to stick. Why? Often its because of exactly what Dan said: the internal navigation makes the home page and second-level pages PageRank-hogs, leaving the third-level pages high and dry.
Some SEOs call Dan’s tactic “siloing”, and attribute its benefits to better themed internal linking. For example, Haylie on Bruce Clay talks about siloing, albeit with a focus on ranking, not index penetration. Siloing, in this case, is done by setting up thematic pyramids via links or directory structure. Just imagine a tree hierarchy, where leaf nodes link up to their parent, then a set of parents link up to their parent, and so on, till you reach the root node.
Dan disagrees: “At the time we all assumed this had something to do with the topics of the pages not being closely related, but we were wrong.” According to him, increase in site traffic is due to increase in PageRanks at the third-tier.
So how do you implement Third-Level Push? In brief:
1. Use nofollow to prevent second-level pages from passing PageRank to each other. This forces PageRank downwards to the third-level.
2. Use nofollow on links on third-level pages to second-level pages so that a third-level page only links to its parent page.
3. Tiered Pairing: To prevent second-level pages from losing too much PageRank, you can link them in pairs: e.g. page A with B, C with D, and so on.
4. Circular Navigation: To circulate more PageRank on the leaf level, link them up in circular faction, so page A links to B and C, B links to C and D, etc.
That’s third-level push in a nutshell.
A Third Level Push Implementation for Wordpress


Does third-level push really work? I decided to give it a shot with this blog as a guinea pig. But how do I implement third-level push on Wordpress? Of course you can just Google for a “SEO Siloing” Wordpress Plugin, but that’s no fun.