[rdorman]

For your set up to work you must have one of the vacuum recovery type caps and the line to the puke tank must always be below the fluid level otherwise it will just suck air. A system similiar to what scott is describing can be found in Carroll Smiths books (cant remember which one) if I am understanding him correctly. But it sounds as though you have what you need, just for some reason the system is not exchanging fluid with the puke tank on cool down.