Hi Reg, If you remember (Or didn't, which is why you posted the question) - The Steam is fed to the slide valve "on the outside" of the sliding body of the valve (but inside the valve chest). When a (White) end port is exposed it rushes into the cylinder through the drillings to the end of the cylinder.
The exhaust passes from the cylinder through the drillings from the other end to the appropriate end valve-port (not coloured) and to the middle port (Nicely coloured yellow by Jason) by passing inside the machined passage on the underside of the sliding valve. It then whistles down inside the cylinder block from the middle valve-port to a side drilling, whence it whooshes out and sprays everyone with dirty, oily, condensate. - Or out of the exhaust pipe to a condenser or oil separator, if fitted.
Why use a picture when I can write a thousand (confusing?) words?