I have watched quite a few liquid cooled videos seen build after build when Linus and Co either stress out about or actually messes up and things leak. I was a utility contractor for years, and that is the experience that makes me wonder why you don't air presser test the cooling system before adding the liquid?
Rig up a T fitting into the system you can use it as a fill hole attach to that a T fitting with a 0-5 psi pressure gauge off the side , connect the other end to a valve, and some kind of air fitting arrangement a Tractor Tire air Valve hose clamped into a piece of tubing works well and you can use either a bike pump or a compressor be sure to turn the pressure way down.
or just buy one of these. https://www.amazon.com/dp/B00IPUCRXK/ref=asc_df_B00IPUCRXK5220065/?tag=hyprod-20&creative=394997&creativeASIN=B00IPUCRXK&linkCode=df0&hvadid=167123274900&hvpos=1o4&hvnetw=g&hvrand=8344412514103572579&hvpone=&hvptwo=&hvqmt=&hvdev=c&hvdvcmdl=&hvlocint=&hvlocphy=9026608&hvtargid=pla-272868395173
it is how they test gas/water /sewer plumbing lines put 3-4 psi on it go to lunch or better overnight and if it holds it will hold air it will hold liquid. way better than running hardware and having to clean up the mess.
