Leaking Propane Connector Valve

Stop right now and do not mess with it unless you know absolutely what you are doing. Any doubt, take it to a shop that specializes in propane tanks. Here is why: if you have accounted for the liquid fill valve, the liquid level bleed valve, tank level gauge port and the vapor service valve (pressure regulators attached here), then what you are describing is the high pressure relief valve. Plug that up and you just armed a bomb. The relief valve may be on the tank separately or integrated on the service valve. The vapor pressure of propane at 127 Deg F is about 250PSI. The valve will vent propane gas causing the liquid propane to boil and thus reduce tank pressure. Never disable any safety device on a propane tank. While we are on the subject, one of the worst practices I read about on this forum is taping into the high pressure vapor side of the tank with a hose to gas appliances. Most RVs will have a two stage regulator that provides gas at about 1/2 PSI (11"WC). High pressure appliances such as BBQ or cookers are designed to work from a propane cylinder or tank with a short hose. A single stage regulator is usually part of that setup. There should always be a regulator on the tank set for the pressure appropriate for the BTU output of the appliance. Without a regulator, a 25' hose will be at the same tank pressure. At 70 Deg F it could be about 100PSI and double that pressure when the temps go to triple digits. At low temps, you could have propane vapor condense in the hose. Anyway, back on topic. Propane tanks older than 12 years may have to be re-certified. It will have to be tested and 'purged' of air before it can be refilled. I have witnessed people being refused to have their tanks refilled because of age or lack of proof of re-certification. Once it was for tanks used on a hot air balloon. I have personally seen a balloon fall from the sky on fire caused by propane system failure. With that in mind... take your tank to a professional.