nkay7 and OrpheumZero have posted illustrations for stories "Sakura's Awesome Experience" and "Melina", specifically for parts where the girls were seated on the toilet.
There are plenty more stories I'd like to see illustrations depicting the girls on the toilet. These include the following:
Avatar: The Last Airbender
A Bender and Her Bowels by Poowrite
Azula's Diarrhea by Poowrite
Code Lyoko
A strange feeling by OrpheumZero
Code Lyoko: Yumi's humiliation
Digimon Adventure
Kari's upset stomach and Yolei's big dump by OrpheumZero
Digimon Frontier
Zoe On the Toilet by OrpheumZero
Dragon Ball Z
Gohan and Videl's First Tender Moment by Poowrite
Pride and Privacy by DrBones
Irresponsible Captain Tylor
Azalyn's Dilemma
Outlaw Star
Outlaw Star: Melfina's bathroom lesson by OrpheumZero
Aisha's enormous shit by OrpheumZero
One Piece
Nami takes a dump by OrpheumZero
Tenchi
Recipe for Disaster by DrBones (Kiyone, Mihoshi, Washu and Ryoko's parts only)
Kingdom Hearts
The Peepshow by OrpheumZero
Naruto
Body Swap in the Hidden Leaf Village by Poowrite
Tales of a Hidden Leaf Bathroom by phil (Sakura, Hinata and Tenten's stories only)
Fire Emblem
Lute's New Hobby by Toasty
Fatal Frame
An Otherworldly Walk-In by Micro
The stories I'd most like to see illustrations of the toilet scenes are as follows,
with 1) being the most wanted and 10) being the least wanted:
1) Tales of a Hidden Leaf Bathroom
2) A Bender and Her Bowels
3) Azula's Diarrhea
4) Kairi's Upset Stomach and Yolei's Big Dump
5) Nami Takes a Dump
6) Body Swap in the Hidden Leaf Village
7) An Otherworldly Walk-In
8) Yumi's Humiliation
9) Aisha's Enormous Shit
10) Lute's New Hobby
Clover, Sam and Alex are all sitting on toilets in the girls' bathroom one day. When Alex touches the toilet paper holder, the floor drops open and all three girls fall off the toilets and down the chute into WOOHP headquarters, still with their pants and underwear around their ankles. The girls scramble to their feet and cover their crotches as Gladis hands to them toilet paper and wet wipes.