Okay, I will jump in here....
OP: I am completely and totally on YOUR side!!!!
You asked WWYD...
You did not ask to be judged and called all kinds of nasty names!!!
There is NO justification for some of these posts here.
IMHO, in no way does not having the ability or desire to clean a public restroom imply any kind of negative label or name calling.
You accepted the position under specific terms, 'no cleaning'... It is not like you are trying to pull something.
I can tell you that I would not be happy to be cleaning toilets either.
I am actually wondering if you may have some personal issues that mean that you just can't and won't. This is probably a lot more common than one might think.
What would I do....
If I thought that I could have a private conversation with the owner, and that this would not be spread around the workplace, I might possibly attempt to have a reasonable discussion.... (only you know these people and how they are likely to react.)
If I had any concerns at all that this would get around the workplace and cause a lot of ill-will with coworkers... and YES, it is likely to do that... Then I would simply turn in my two week notice. And, I would indeed be looking for another position, asking at interviews for detailed job description requirements......
If the owners press for a more specific reason, then you can tell them, again, that with the change in job duties expected, that you feel that you can no longer fulfill the requirements of the job...
THIS IS, ACTUALLY, YOUR ISSUE, AND NOT THEIRS.... IT REALLY IS NOT THEIR PROBLEM IF YOU FEEL UNABLE TO DO THE ADDITIONAL JANITORIAL DUTIES. SO, YOU SHOULD JUST SIMPLY 'OWN' THAT. YOU NEED TO TAKE OWNERSHIP HERE. POINTING FINGERS ACCOMPLISHES NOTHING.
YOUR CURRENT STRATEGY OF MAKING THEM FIRE YOU IS COMING FROM THE WRONG DIRECTION. TAKE OWNERSHIP OF YOUR OWN PERSONAL DESIRES/ISSUES.
TALK TO THEM IF YOU MUST, BUT THEN I WOULD ADVISE THAT 'YOU' MAKE YOUR OWN DECISION ON WHETHER TO STAY OR GO. ONCE THIS BECOMES ANY KIND OF A SORE POINT, YOU WILL NOT BE LEAVING UNDER GOOD TERMS... NO MATTER WHAT.
PS: I would seek a position where there there are janitorial positions on staff or on contract... this would be most likely to solve your issues.