Depends what's blocked it. Without going into the gory details, leaving it overnight can soften paper and tough turds. If it's more serious then it's probably a dismantling job.
It's possible this has happened because of a gradual scaling up, which does happen, particularly if the crew don't take care to flush out well. Urine leaves scaly deposits which gradually reduce the available bore.
My 5 year old Jabsco blocked for the first time 2 weeks ago. It was blocked at the right angled bend on the outlet and was caused by loo paper despite the fact that I always use Aqua-whatever-it-is. It's obviously an unpleasant job but straightforward job to strip down and while I was at it I replaced the top gasket and valves.