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.
1It is not clear from the OP which is the author's intent.
10http://www.cygnus-x1.net/links/lcars/blueprints/uss-enterprise-fasa-15mm-deck-plans-sheet-5.jpg Seems some of the toilets are actually ludicrously spacious. ;) – fgysin reinstate Monica – 2016-12-06T08:45:07.790
2@fgsin Well, that looks like a very nice but completely different starship to the one I'm considering. – Joe Bloggs – 2016-12-06T08:53:55.813
2
I know that any comparisons to existing starships are purely coincidental, but Enterprise, Voyager and Enterprise-D did actually have toilets. In fact, Voyager once had a comment about only 4 functional toilets remaining during their trip, and Officer Riker at one point said the Enterprise-D had only 1 toilet: https://io9.gizmodo.com/5318344/wheres-the-bathroom-on-the-enterprise-9-space-toilets
– Nzall – 2016-12-06T10:54:15.20715@fgysin The bathrooms seem to have pair toilets without dividing walls, which is surprising. I guess social values around privacy while pooping have changed in the 24th century. – Oliver – 2016-12-06T12:39:38.703
34Plot twist: Entire crew is actually robotic. All the metal bits are hidden behind material pretending to be skin. No one is aware of the true nature until it becomes a plot point. – M i ech – 2016-12-06T13:24:10.330
2Who needs toilets when you have airlocks? – Z.Schroeder – 2016-12-06T15:53:19.437
3It wouldn't be very exciting if you weren't perpetually at risk of soiling your underwear – bye – 2016-12-06T16:10:16.947
2Don't forget that toilets are also very useful for vomiting! Even if you figure out how to eliminate bodily waste, you also have to figure out where the crew is going to puke. – Mohair – 2016-12-06T17:58:47.077
11
I always assumed all the chairs on the bridge functioned as toilets, and that crew uniforms were just stylized union suits with an auto-connecting rear flap. The most staggering part of this insight was the accompanying realization that the entire crew spends their working day in their pajamas.
– brichins – 2016-12-06T18:21:44.0003
See also Are there bathrooms on the Enterprise? and Where does human waste go when going to the toilet in the Star Trek universe? on the sister site for Science Fiction & Fantasy.
– Rand al'Thor – 2016-12-06T20:58:54.0238@randal'thor Those questions most certainly did not inspire this one. No sir. Not at all. Ahem – Joe Bloggs – 2016-12-06T21:53:17.120
1Maybe they all just love pooping on the floor. It could be their species's Thing: pooping on the floor. – user2357112 supports Monica – 2016-12-07T06:50:19.093
2I have no first had or bottom knowledge of TP or early means for elimination of pre-processed organic byproducts. I do know that NASA is offering 30K for the best idea to process/remove/transform Astro-poop. Check NASA site for your ideas to be perused. – user30555 – 2016-12-06T13:22:28.750
1My guess is that all the crew are robots that never eat or poop. – b_jonas – 2016-12-07T13:20:21.183
2astronauts use Depends underwear? – LeHill – 2016-12-07T21:03:14.540
2@Oliver, I would charitably assume that the second "toilet" is in fact a bidet. – Eike Pierstorff – 2016-12-08T12:10:51.787
3It is where the Captain's log is stored.... :) – Old_Fossil – 2016-12-09T05:36:53.517
1So many good answers! Chosen one just because I still laugh when I read it. – Joe Bloggs – 2016-12-09T07:50:46.900
@John: sorry, your tinypic link page has banner ads containing malware – smci – 2016-12-12T10:39:38.363
@smci, my apologies, I'm glad someone caught it since I didn't. – John – 2016-12-12T17:19:19.930
1Advances in nutritional science have resulted in food that no longer produces solid waste. Instead, everything not absorbed by the body turns into gas. – EvilSnack – 2017-04-15T16:58:15.807
2Everyone who mentions the need for a toilet receives a red uniform...problem solved. – Klaws – 2017-10-23T12:13:38.240
Toilets don't work in space. That's why there aren't any. – Mazura – 2019-04-26T09:23:56.437
@Mazura: Wow. The people on the ISS must be backed up something fierce! – Joe Bloggs – 2019-04-26T10:15:37.950