There is a way to plug the rodding hole - not using a test plug, but I don't want ree to abuse me so I'm keeping quiet for now. But you mention 2 manhole covers - what's the second one do ?
For the new hole hire a diamond core drill and tool to power it . You could use an sds drill IF it's got a clutch - to power the core drill. You might get a circle of render to put in the original hole.