ENV: I am running tmux in putty, on a windows 7 laptop. I do ssh to linux systems while working.
I have to solve two glitches with tmux, before using it for all my needs.
Assuming mouse mode is already on, add this to your tmux config and selecting will now copy to your clipboard.
bind -Tcopy-mode MouseDragEnd1Pane send -X copy-selection-and-cancel\; run-shell -b "tmux show-buffer | clip"
Tested on v2.6