Update & video:::
Well I have filled it up with freshwater and so far it looks leak proof!
I may redo the ATS slot pipe as its not coming out as even as I would like, and it's noisy. I think I made the slot too wide, kinda hard with a circular saw on your lap while squinting!
Looking around for something to use as a splash guard around the ATS, although it may not splash so much if I make a more even slot pipe.
Need to add some rubber washers or something under the skimmer and return pump as they rattle on the bottom of the sump tank.
The emergency drain works perfect of I block up the slot pipe.
Going to keep it running for a couple of days to test that nothing leaks.
Here's a short video, I will post a better one with my real camera once it's all complete, busy right now...