I. Improved food
Finally, they are here. The nutricapsules are scientifically designed to be 100% absorbed by the guts, leaving no organic rests to be "disposed of".
This allows your spaceship to store enough food for the mission in just a few modules, with no need of the extra weight associated with traditional food, as:
food that is only useful in 25% of the weight (if lucky).
facilities for storing the food and/or grow more.
facilities for waste treatment (including WC) and recycling.
Some minor inconveniences are the adaptation periods before and after such a diet, to train again your digestive system to deal with traditional food.
II. WC at battle stations
If the objective you are after1 is ensuring that nobody leaves their post while they are on duty due to "technical emergencies", then the other way around is make everything (at least in control positions) a WC.
Technical suits have the appropiated "connectors", both to the wearer's body and the control chairs, allowing a unconspicuous, odorless and silent "emergency evacuation". While most astronauts prefer the solution with pill foods and think of this solution as a solid #2 (if you get what I mean), more than one has found this method surprisingly useful when fighting against overwhelming numbers of flesh-eating Zampas.
III. Surrogate crew members
Space travel is long and dangerous, and a body subject to it will suffer greatly if not properly protected. But to be effective, regular work in unsafe places of the ship is required, and robots are just not effective enough yet.
So the crew members are safely stored in a semi-stasis state, with their body functions unoperative until it is time to end the journey. Their mind, though, is fully functional and is wired, through the ship systems, to a robot "crew member" that he will direct with his thought. To improve control, the robot will be anatomically very similar to human.
While functional, this arrangement was object of some criticism due to the long, long hours of boredom while the robot work was not needed. In an effort to alleviate them, the last generation of robots has been granted the ability to drink beer and has had some modifications done to the body, adding to the design certain parts that were left out from previous versions due to their lack of perceived usefulness and a certain degree of puritanism by the builder.
It is not clear from the OP which is the author's intent.