Here's our inspection chamber. We tested (not scientifically) the flow of water from a watering can, and it flowed out the right end, which was nice.
So all that's left to do now is install the dpm over our beautifully smooth flat sub-base, some Flexcell board around the edges, and get another 20 tonnes of concrete in there!
One more quick thing - if you've posted a comment and it looks like I've ignored you, I havent - I literally didnt know that facility existed on this blog! It's only looking at a list of posts to edit one of them that I saw that some of the previous posts have '1 comment' written next to them.