I will try my best to awnser both questions but it has been a while since I have played this game. Also, I will go over the nicole toilet route first in this post, however the gwen and nicole toilet route is the same steps but you must do something before nicole toilet route steps. Read the entire post before you try to attempt these steps in case you want only one of these endings.
First is the normal Nicole toilet ending, this happens only on the you chose to save your brother route at the dance/party thing. After you follow what Ariah says for a bit, you get to a point where u need to hide drugs in Nicole's Room. If you hide in the closet, Nicole will find you, at that point you choose to completely spill why you were there. If you do this, nicole will do a partial toilet scene (if I remember right) but not scat and instead period blood. You will be asked if you want to see hardcore content and need to pick yes for the ending you are wanting.
After this scene, Nicole will be on the look out for Ariah who is hideing behind the dorm building. If you talk to Ariah and then head back to Nicole and reveal Ariah's location to Nicole, Nicole will get the idea that all it took to break you was the toilet slavery. Progress from here by checking back on Ariah's location (which she will be missing from) and then continue as normal. The next day you go to class and Ariah is still no where to be found, however a lot of the girls will comment on how they are looking forward to tonight. When you go to sleep, you will be ambushed at your door and get a scene where most of the girls in the story use you as a toilet. After this you wake up on the final day.
This is the part where you can have either just a nicole toilet ending or a nicole and gwen toilet ending based on your choices before. If you didn't date gwen, then you can just go outside to find nicole and get the normal toilet ending. If you date gwen and then check the library (stairs at the far left in the school), she will be there and give you the option to potentially get back together someday or leave her forever. She only appears I think the day after the ball so if you don't do this then you wont get the other ending. If you did talk to her in the library before all the steps with nicole, then the ending will include them both.
The nicole and gwen ending isn't much different but it is still worth it overall, I wish you luck and if you have any questions let me know.
