There are two basic approaches to the ofuro drain design:
1) Without overflow. Traditional ofuros simply have a floor drain and no overflow system. This allows the tub to fill to maximum depth, right to the rim, and potentially overspill. This means that the floor under the tub must be waterproof and have a drain to handle overspill.
Good options for a floor drain are trench drains, trough drains, indirect drains or channel drains.
The ofuro drain is shown in the photos below. The size is 1.5" NPT (standard pipe thread), and the closure is a swivel top with o-ring. Finish choices available.
2) With overflow. If the traditional method above is not practical for your design, choose the optional overflow drain for a system that prevents the tub from overspilling. The overflow drain is an external fixture that limits the water level in the tub. Use of the overflow allows the ofuro tubs to be installed without the need for a drianing floor area. Finish choices available.
Images below show the overflow fixture parts and installed.