I have the same problem with the added issue of a concrete drive laid on top of the existing level so the DPC is only 5mm above ground level. I am digging out concrete around perimiter of my house, as a temporary measure, until I can afford to lay a new drive and hacking off the render to one brick obove the DPC, I am also cleaning out the cavity by removing a brick every 3 bricks and putting my hand in and scooping the **** out (suprising how much bther is). I am going to inject a new dpc to the inside wall ( I was persuaded in to this). And then I am going to cross my fingers and toes. I was also thinking of having the outside of the house clad in insulation as the walls are very untidy now, I had the wall ties done about 3 years ago which has left them patchy. I just saw the date on the post. What did you do after.
Use wet & dry vacuum, use one to remove soggy insulation from the cavity. No tools or extension pipes, just slide the hose along the cavity.