With a non recovery type system there is supposed to be an air gap in the radiator, and if it's filled all the way it IS going to push coolant out.
When it does it'll push past any cap you put on it.
A recovery type system lets coolant expand (like it's going to do) but then pulls the expelled coolant back into the radiator when it cools down and contracts causing a vacuum.
One other thing to realize, is that whatever amount your engine normally pushes out weather it's a recovery system or not, the tank needs to have the capacity to hold it or it IS going to overflow the catch tank.
I just ordered this one to replace the old plastic one.
I have a recovery system on it already, but just want a better looking tank.
Note the capacity.
http://www.jegs.com/i/JEGS+Performance+Products/555/51136/10002/-1
Of course after I ordered it they said it was back ordered and will take an extra couple of weeks to get it, but like I said the existing system works but is just ugly.