tmux is super handy, even if you don't own the box.. so, you might be motivated to compile it locally if you need to get some stuff done
it's not too difficult, but requires a non-trivial amount of RTFM
anyway, let's say we want to do the build in ~/dev
git clone https://github.com/ThomasAdam/tmux.git ~/dev/tmux_git
is your first step.. in the ~/dev/tmux_git dir you can do ./autogen.sh which should get you a configure script.. now, if all the libraries and stuff are already on the box then you could just do ./configure && make and have a functioning tmux, generally though, there'll be a few missing dependencies, libevent seems to be the most commonly missing one though..
this means we also have to build libevent and maybe ncurses locally, which, if you made it to here is probably where you're stuck.. download the .tar.gz files, build them locally, doing something like:
./configure --prefix=$(echo ~/dev/)
followed by make && make install
you should hopefully by now have all the include files and stuff required for building tmux.. (double check you have ~/dev/include and ~/dev/lib containing stuff like event.h and all the .so files..
finally to compile tmux.. if
CFLAGS="-I$(echo ~/dev/include)" LDFLAGS="-L$(echo ~/dev/lib)" ./configure --enable-static
and make work without any complaints.. you should now have a tmux executable in ~/dev/tmux_git/tmux, which you can create a soft link to in ~/.local/bin or somewhere else in your $PATH