Overflow bottle question

This is what I have got. Thanks to all that can help. I purchased a billet overflow bottle from summit. I noticed it does not have a vent in it. It has the nipple in the top for the hose and a valve on the bottom. I am having an issue with my dart. Pressure seems to be building up in my cooling system. I replaced the head gaskets this week and found several bolts not tightened properly. With that said I still feel the hoses have to much pressure in them. This is what I think is happening. I flip the lever on top of the cap at operating temp. and it does not vent to the overflow. I bought a new cap [16psi] and same result. I opened the valve on the overflow and walah pressure in the overflow. After evactuating the res. the cap will now vent. I think the pressure that is being let off from the cap is pressurizing the overflow to the point where the radiator and res have the same pressure and no more venting can occur. question is should I drill a vent hole in the top to relieve pressure? I think it needs a vent. What are your thoughts? Thanks Tod