So the loop is complete and the air pressure test passed with, in my opinion, flying colours. There was not even a tiny drop in air pressure on the tester in over 3hrs and I'm sure there will be mixed opinions on wether that's long enough or too long but for me I thought it was adequate. Due to the amount of fittings I used to get the look I was (sort of) going for I was quite nervous about wether it would pass the pressure test. Thankfully all the extra time I spent basically polishing the hard tubing where I made my cuts was worthwhile as they all fit together perfectly and there was not one damaged O ring in the whole build. Unfortunately the two runs from the GPU have some sag in them due to the weight of the fittings and the flow meter. I will address this at a later date, probably when I either empty and refill the loop or when I decide how to better design the runs themselves.