Now go and get yourself a power supply tester; this little device will allow you to switch your PSU on without having to wire up your motherboard and will save your ass in the long run, should the system leak and get onto your components. So long as no power is flowing through the motherboard or any other components, if they get wet then you should be able to dry them off thoroughly and all will be fine.
Fill up your little fill bottle so you can get the nozzle into the fill port and start filling up the reservoir to the max line. Then turn on the power supply tester to turn on the water-cooling system and watch all the green liquid drain away into the pipes.
Once your reservoir is empty, turn the power supply tester off and fill up the reservoir again to the max point. Repeat the process until the reservoir never completely drains and then at this point, top up to the max fill line.
As you can see in the pictures, I have wrapped tissues around each join of the tubes to ensure there is no leaking; it's a sensible move to do this and run your system for 10 mins to test and make sure that the tubes are properly connected.
If you have a flow meter on the system, like the one mounted in the front of the 3-bay system here, you can sit and watch its hypnotic swirling.
After the testing period, you can remove and inspect all the tissues for leakage. If all is good then you can install all the other components and hook up the system.
Congratulations, you have a fully water-cooled system!