I have collected some information on Sumo over the years since I competed in a few amateur tournaments (they were held by the national amateur wrestling association while I was competing in Greco and Freestyle, so I entered both in the lightweight category and the opens for sh*ts and giggles).
While training in the stables varies, it usually contains a few staples: shiko (stomping and squatting, often for 300-500 reps) and a sort of sliding duck walk (suri ashi) for the legs, as well as push-ups (see
– this guy is a high school Sumo player who has an entire series on Sumo exercises) and Teppo (slapping a pole) for the arms. Plus sitting in the splits – Sumos are often remarkably flexible, it helps with their wide and low stance. See here:
SUMO TRAINING and
Apart from that, there are of course wrestling bouts, technique drills and various partner exercises – some shown in the last link. There's a ton of Sumo training footage on Youtube, you should be able to find it with the terms provided.
Some Sumos will also use rubber bands for rehab and prehab, some lift heavy weights (some even move respectable weights powerlifting style) or use machines, but more commonly they do higher-rep stuff with light (10-15 kg) dumbbells, mostly pummeling, curls and duck walks. I have also read reports about dragging tractor tires uphill (with another Sumo riding the tire) but I’ve never seen this. This would however be similar to pushing a person around in the ring. Top Sumos are often remarkably good sprinters, probably mostly due to selection, but also due to the explosive nature of their sport and training.
One thing to always bear in mind: Sumo is a wrestling style, first and foremost. The exercises they do are intended to complement their wrestling practice (not the other way around) – just like in every wrestling tradition ever, regardless of what time or part of the globe we’re talking about. Therefore, taking the exercises and leaving out the wrestling part is going to yield totally different results.
Cheers
Period.