"Iron Maiden" Bathtub

This bathtub has two large metal parts that are hinged like the classic "Iron Maiden" torture device (linked), except that it is mounted horizontally like a coffin. Each part contains a liner that constructed to closely match your body's form. The liner is removable; different people in the household have their own liners for this bathtub.

When you climb in and activate the closure sequence, your head remains outside the tub. You will use voice commands to specify various events, of which, obviously, one of the most important is the command to open it up so you can get out, after your bath is done.

When closed, the liners mesh and seal tightly. There will be perhaps one millimeter of space between your body and the liner, except at the neck area, where flexible material is used to seal the tub-opening there, where your head sticks out.

Perhaps you have heard that you can theoretically float a battleship in a cup of water (link)? Basically, if the battleship is placed in a precise hull-form-fitting container, water in-between the container and the ship can be very small in quantity, yet the ship can still float in that water.

Anyway, the advantage here is not so much about floating, but minimizing water usage while taking an actual bath. With voice commands you specify that soapy water should be injected into the space between your body and the liner of the bathtub. There should be both inlets and exits, and a flow of such soapy water should be able to clean you quickly.

Then you command the rinse sequence to begin, and next would be a drain sequence, and finally there could be a pressurized warm-dry-air breeze, after which you open the tub and climb out.