A stupid toilet joke from another post, a snow day, and a stronger edible than I was expecting got me wondering: have we ever seen a 24th century Starfleet toilet, and how would it function?
Edit: I meant 24th century / 2300's and not 23rd century.
Background
I know we've seen the sonic showers which seem to operate similar to, but also different from, a regular shower, but I don't ever recall seeing any other typical bathroom fixtures in the 24th century Starfleet vessels (well, mirrors still seem to be just mirrors, so there's that)
The only references I saw on Memory Alpha for the 24th century were:
- A very blurry, zoomed-in shot of a section of the Enterprise-D when the Borg cut away a section of it.
- Lower Decks where Boimler drops his tricorder in the toilet (Note: I am in-between P+ subscriptions until Disco comes back, so I can't reference the episode for evidence)
- Various references to "waste extraction" on vessels of other civilizations
A very blurry shot of what Memory Alpha claims is a toilet on the Enterprise-D
For the purposes of this episode of Shitty Daystrom, we'll only focus on Starfleet's facilities.
Would toilets still be the same as we know them, familiar but different, or something more exotic?
Option 1: Same As We Know Them
Without any evidence to the contrary, it would be relatively safe to assume nothing has really changed on that front between now and the 24th century. Furthermore, water conservation isn't much of a concern due to replicators existing. The waste would be carried via sewer pipes, similar to what we have now, to a waste reclamation system (which may operate differently but do the same thing as treatment plants we have now).
Evidence for this includes VOY: Projections where "sewage and waste reclamation" was a system that was reported to be offline when the computer was queried for a status update. While the episode existed in a malfunctioning holodeck program, there's no reason to assume those systems don't exist on the real ships.
I'm not a fan of this assumption since it would imply a huge lack of innovation and would be generally inefficient given other technological advances at their disposal. The supporting evidence is also vague in that it doesn't specify whether "sewage and waste reclamation" was a central or distributed system.
Option 2: Familiar But Different
As mentioned above, "sewage and waste reclamation" is a subsystem that exists on Starfleet ships. In this model, rather than being a centralized system like a treatment plant, it would be a distributed system.
The restroom fixtures would remain more or less familiar to what we have now, but instead of physically carrying the effluent away for central processing, they would simply dematerialize it and reclaim the energy (like putting your dirty dishes back into the replicator). This would simplify the engineering requirements and reduce mass since the EPS network is readily available; no extra pipes would need to traverse the ship.
Alternatively, instead of directly converting it from matter to energy, it's beamed from the fixture into a central processing unit. That seems inefficient to me because of the extra and unnecessary step of re-materializing it.
Option 3: Something Completely Exotic
I grant that this one is more of a stretch, but bear with me. Instead of anything we're familiar with, it would simply be a special type of transporter which locks onto your waste and just beams it out of you. From there, it's either immediately reclaimed as energy and stored or transported to a central processing unit for bulk conversion.
As said earlier, this theory is a bit out there, but with the one-piece uniforms, I can see how they would be practical.
Conclusion
Without the ability to reference the Lower Decks episode 'Grounded' for possible additional evidence, I'm going to stick with my personal head-canon of Option #2 as the standard Starfleet waste reclamation method. The reasoning is based on how I see the available technology being best utilized and the efficiency at which that method would operate.
We saw one in Star Trek V when Kirk, Spock, and bones are put in the brig of the enterprise – a. Kirk pushes a button and it slides out and he sits on it. But the lid is down, and thankfully, he doesn’t use it. It kind of looks like a normal toilet. That’s all we know. 
To be fair (and pedantic) that is a 23rd century toilet.
I commented before OP edited his title and post. Originally, he was asking about a 23rd century toilet.
Yep, that's on me. I confused 2300's with 23rd century and had to go back and fix that.