First, whether you're on carpet or hard floor, I recommend putting a set of large glides under it. This gives you a fighting chance of partially de-watering and moving it at need.
Second, you may consider a set of concrete blocks between the tank and the wall, which will give a fairly svelte person a chance to step onto those and wiggle a way to the box.
Third, a mirror aptly tilted may let you see into the box.
Fourth, a good painter's ladder may help access the unreachable.
Fifth, access to the overflow box piping, standpipe, et al, is usually by lying on one's back inside the stand and doing the connections from below.