My tmux configuration file is as follows:
unbind C-b
set -g prefix C-v
bind -n M-p split-window 'ftpane'
set-option -g mouse on
setw -g mode-keys vi
set-option -s set-clipboard off
bind P paste-buffer
bind-key -T copy-mode-vi v send-keys -X begin-selection
bind-key -T copy-mode-vi y send-keys -X rectangle-toggle
unbind -T copy-mode-vi Enter
bind-key -T copy-mode-vi Enter send-keys -X copy-pipe-and-cancel 'xclip -se c -i'
bind-key -T copy-mode-vi MouseDragEnd1Pane send-keys -X copy-pipe-and-cancel 'xclip -se c -i'