So it turns out that donated troops work only in defence, but in attack you use what you normally have. This doesn't really make sense. Confused a lot of my clan members!
If you send out a request in the clan and receive for say 3 lvl 1 giants, then those may only be used in attack (and defense, although not clan war defense) as you had to send out an actual request for the troops. You receive defense in the clan war only troops by getting troops donated to you in the area in clan wars. Hope that I cleared everything up for you!