If you take the pipe off, you'll have to make or buy a new gasket for it. Taking off the clamp won't make it more mobile if one of the three allen bolts is still attached tightly. I'd first check the plugs with a mirror while it's hooked up the hose. You can feel the plugs if you can't see them. Also, you can dry off the pipe and check by running a paper towel (or something else dry) over it to check for leaks.
If you're still determined to take it off, I'd suggest using the long end of the allen wrench at a slight angle. Get it in there as deep as possible and apply a breaker bar to the short end to increase your leverage (a small socket with a 4" extension works really well for me).