Just tested it out and here are some example commands:
set Player bowels_capacity 10000 -sets the players capability of holding stuff in their bowels to 10000
set Aria stomach_capacity 10000 -sets Aria's capability of holding stuff in her stomach to 10000
set Amber bowels_water 5000 -sets the amount of water in Amber's bowels to 5000
Just play around with names and the autofill.