Now that you have built your loop (single loop) you have to fill it and test it for leaks. This was not covered in the How to build a custom water cooling loop because of the length of the Tutorial and all the steps needed to build the loop.
When you built your loop you needed to make sure that you had two ways to access the liquid in the loop.
Fill ports and drain ports.
Filling and draining. Different color liquid can match an overall theme.
While the loop will stay closed once filled you do have to provide a way to get the liquid in and out of the loop. For the long term a good maintenance habit is to change the liquid every 6 months. You also need to provide for the condition of the liquid and prevent the growth of microbes.
Choosing the liquid for your loop is strictly a personal choice as there are many liquids available and colors. Some will come already with a color while others come clear and a good clear liquid is Distilled water.
I prefer the clear liquid with the option to select a dye color and make the color to my preference. Currently I have a Blue theme and I can make the liquid inside the tubing as light or as dark as I choose.
Filling your loop, is where you will start the process of getting the liquid inside the loop. The spot that you have designated as the fill port is where you will pour the liquid into the loop. It would be a good thing to have either a funnel or another type of tool to ensure that there is not any spillage.
I have found that the bottle works the best for me since it has that long flexible tube on the top where you can get at the top of a reservoir that may be inside the case. If you put a fill port at the top of the case with a hole and fitting set up then a funnel will work for that.
Make sure your drain port is closed and the power is disconnected from the wall. You can also place paper towels or clean soft cloths at all the blocks and fitting areas to catch any leaks. Fill slowly while checking for leaks so you can catch them right away. Pretty much leaks will happen when a fitting is not tightened all the way or a clamp is loose.
When filling the loop you will get to a point where you will need to run the pump to start filling areas of the loop that have air pockets. A good place to be filling is the reservoir since once the pump is run that's where the air will have a place to go. After checking for leaks you can connect the power supply and take the main 24 pin motherboard connector and unplug it from the motherboard. Take a wire jumper or paper clip and insert one end into the hole where the green wire is and the other end where a black wire is , there are a couple so any one will do, however there is only one green wire. This will activate the power supply and provide power to the cable connectors and by connecting the pump you can run just the pump and have all the other connectors unplugged. This way you are not providing power to any component and the motherboard so that in the event of a leak nothing will short out and you will be able to dry everything off.
Now that you have liquid in the loop and you run the pump you will notice that the liquid in the reservoir is getting low and then going dry , don't let the liquid level disappear all the way , stop the pump and fill in some more liquid then start the pump again and repeat this process until the level seems to stay. Check thoroughly for leaks, use a flash light if you have to because you do want to catch any and all leaks if you have any.
At this point you can add some biocide or a silver coil (the silver coil will fit through the opening on the top of the reservoir just remove the plug if you put it back once you were done filling). You would not want to add the biocide before checking for leaks to not waste any if you had to refill.
This silver plug is a nice option but it does want to be installed on a bottom port on the reservoir before filling, putting it in a top port will not help unless the reservoir is completely full at all times.
Once the loop is completely full you now want to run it for several hours, the recommended length of time is 24 hours so you can follow that or choose to run it for less time but the longer you can run it the better. After running the loop for an extended period of time you will now notice that the once full loop is not full any more and that's because by running it for a loner period of time you have released more trapped air, most likely from the radiator so you can add some more liquid to get to the full point.
You should keep an eye on your liquid level as that can get lower if there is any more trapped air or if a leak develops that can be the first place you will notice it by a lowering of the liquid level.
Water cooling loop maintenance is a good practice to get into, just because you built this custom loop doesn't mean you can just think it will take care of itself. The liquid should be changed every 6 months and while it's not mandatory to be exact it is a good idea to change it around that time frame. Add a drop of biocide and I do mean a drop because that stuff is powerful and poisonous so be careful with it. If you used the silver then you don't need to change anything.
Remember this is a custom loop and anything can be added or changed to suit your needs. Two web sites that have a big selection of water cooling parts are;