Not sure if this has been done before or not.
My water loop isn't a traditional water loop. With that said, when I need to drain and refill it, I usually get a mouth full of water because it's difficult to get my pump primed enough to run with gravity only. After looking though some DIY power bleeder setups to change my brake fluid, I thought it would be perfect for the cooling loop in my PC.
Anyway here it is.
Smallest pressure sprayer @ lowes
female g1/4 coupling (I had some bulk head adapters laying around)
2 barbs (also had laying around)
Clamps (Probably not necessary)
Originally I was going to cut off the nozzle end and just throw on one of my barbs at the end of the sprayer hose, but I realized that I could attach my bulkhead adapter to the end of the nozzle. It's obviously not g1/4, but close enough to allow me to thread it nice and snug. I'm probably not using more than 3-5 PSI, so it works fine.
I just hooked it up to my drain, opened my fill port, pumped the handle 4 or 5 times and slowly pressed down. Once the reservoir filled up, I ran the pump until it hit an air pocket. Shut it down and did it again until the pump could run freely.
I only have my reservoir and both rads in my loop now, but I don't see the water blocks keeping this from working in the future.
Also helped in draining - opened the drain and used the sprayer to blow air through the system.