[GigaFrog]

Put a Tee connector at the lowest point of your system (if you have a reservoir, just put a fitting at the bottom side of it). The 3rd output of the Tee is connected to a long hose (~2 feet) which other end is closed by a cap. This is the flush end.
Do the same thing at the highest point of the system. This is the bleed end.

To empty: Take the flush hose closed end down below the computer and open it to flush your water is a bucket. Open the bleed tube up above the computer to let the air come in. The water should flush quite quickly.

To fill up: Keep the bleed tube open, high, and not on top of your system (water may come out of it, put a small bucket under it).
Take the flush tube high up, and fill through it. Once it is full, run the pump to flush air pockets. That should fill up with minimum air pocket.

Personnaly, I have more problems filling up that flushing. This system is a bit complex, but should ease filling.

Good luck.