A new but effective procduct is the 500ml LDPE spray bottle. The tip fits into the plug & cool tubing and also into the G1/8" connectors. The spray bootle will enable you to easily fill your system.
If you own a aquatube or aquabox you plug the tip of the spray bottle in the sucking connector, press the bottle and wait until the water comes out on the inlet connector. That will take less than 30 seconds and usually no further deaeration is required.
The bottle will cost 3.99 Euro.
A few pictures: