The vast majority of a sumo wrestler's training bouts take place at home, against his own stablemates.
This works well if, like Terutsuyoshi, you join a powerful stable filled with top-class opponents of varying shapes and sizes. It allows you to go up against rikishi far better than you every morning. There is no faster way to improve than being tested constantly and never allowed to become comfortable.
If a stable is small with only a handful of rikishi, degeiko (outside training) at a nearby stable may be more common. Kakuryu for example spends a lot of his practice time in Tokitsukaze stable just down the road from his own Izutsu stable.