Originally Posted by Old-Biscuit
Which toilet brand/model?
Might be as easy as changing vacuum breaker module OR just opening 'stub' (drill bit) on existing vacuum breaker.
Lot of them have the stub but are sealed unless optional sprayer is used.
I have a Thetford, Aqua Magic Style Plus or Style II (In my owners manual they're so busy accommodating all the language options they forgot to differentiate between the two). I can see the vacuum breaker on their exploded diagram, of course it's on the backside of the toilet.