I never use bags for grain or hops. You need a good vigorous rolling boil with the hops loose in the boiler. Yes, it does mean you have to clean them out afterwards. The first boiler I used was a 6 gall tea urn. Open the tap slowly and you shouldn't have too many problems. A word of caution: when I wanted to replace it I found the new ones had taps which wouldn't stay open. Yes, our old foe health and safety. I returned it and bought a proper one from The Homebrew Shop which is excellent. It has a proper pro tap and also a device called a baxooks which strains the grain and hops allowing the wort to run freely. It really is superb. With grain, again if you want a decent extract the grain is better loose not bagged.
