Put it wherever you want the air to end up, so generally in the top of the reservoir, that way it's easy to take it off. Same with draining put the tube on, turn it over. It won't be really fast unless you have somewhere to let the air in/out to displace the water.
That's why it can be good to have a drain valve as it gives you somewhere to attach a hose that is 'under' the coolant level before unleashing it (doesn't have to be the bottom) and then you can remove the bung from where you filled it (where the tiny bit of air is) and all of the coolant will fly out. It's not critical that the drain bung/valve or whatever is at the absolute bottom, because you can still turn the rig over. So just put it somewhere you can get the most coolant out possible.
At the same time, especially in a simple loop you could do that easily with no valve, save buying some fittings and the trouble of doing something pretty with it. Fittings are expensive and the easiest way to go hugely over-budget, once you go into that monumental inventory of Bitspower you can say goodbye to your rig building money.
Buying a PC is like buying the car, if you get a good one or a bad one once you get interested you will spend money it, that's just unavoidable. You know the amount of insane money people spend on making something faster or prettier and that applies to both. By the time your considering watercooling you probably have way too much money in your PC from the perspective of a civilian.
JR
