Trying to add an interaction to terrain but it's causing a route failure

Well, from the stuff I've dealt in recently, special situations with posture will have a generic_ interaction as one of the affordances on the object that looks something like this:

  
    
      
        Object
      
    
  
  15540
  
  False
  False
  0.5
  
    
      
        
          Actor
        
      
      
        
          Object
        
      
    
  
  False
  
    Interaction_Super
    Interaction_All
  
  NORMAL
  1
  OBJECT
  
    
      
        
          26171
        
      
    
    
      
        
          
            CHILD
            TEEN
            YOUNGADULT
            ADULT
            ELDER
          
        
        
          
            
          
        
        Actor
      
    
  
  30
  False

So if you're making a new/modified posture, you might try creating a custom version of this interaction and add it to object_terrain super_affordances, with the _provided_posture_type being your toilet stand posture, instead of Maxis's. (Not sure terrain is treated in the same way as most objects though.)

Or maybe try adding it to postures.posture_graph in the POSTURE_PROVIDING_AFFORDANCES section.