In many clans, low level players donate troops which are not useful in war.
My idea - When you click on the clan war button, it should say who donated you in your war castle and what did they donate. Similar to the notification we get when someone donates us normally.
Send out a clan message that says only certain troops to be donated in war cc's. And if someone does put troops you don't want in there, you now have the option to remove them. Not really necessary unless you have a member trolling your clan and constantly putting gobs in, and is always online to put more in when you remove them. Hilarious. Best Regards.