Using a combination of PVC and SpaFlex, the plumbing has lasted years without issue.
The 400g's plumbing needed to look sleek to match the rest of the system. For now, all the documentation on ReefAddicts is linked below:
Return line to Penductors (2011): http://www.reefaddicts.com/entry.php/1285-Plumbing-Return-assembly-with-Penductors
Return line to Penductors (2013): http://www.reefaddicts.com/entry.php/28974-The-400g-is-officially-running-(Blog-500!)?bt=45774
Inside the fishroom, the large vertical poly tank holds 250g of saltwater that is constantly in circulation. It is mixed up with synthetic sea salt (Sybon Reef) each time it is refilled with RO/DI water. To make water changes easier, I ran Spaflex tubing from the circulation piping to the sump, installing it through a Uniseal fitting. All I have to do is open a valve, watch it fill up, then close it until next time.
Here's a video showing how I use the REVERSE check valve method with penductors, and why