To answer as simply as possible, I would point out that you are changing the meaning of the sentence when you add that as you suggest. Those thats are not implied, nor are they missing from the original sentence. Don't redesign a sentence if you don't understand it; you have to take it as it stands and see what you can make of it.
As it stands, it is quite a simple and commonly used construction. Keep in mind that "find" is a transitive verb which takes an object. In this case, the trick in understanding is that the object is not the toilets themselves, but the condition of the toilets. The management hopes that what you find is their good condition. It would, however, be slightly awkward to say "we hope you find the good condition of our toilets," so they say it thus: "we hope you find our toilets in good condition." And yes, you could say that they want you to find (discover, learn, realize, come to know) "that the toilets are in good condition," but what this really MEANS is they want you to find the fixed, static, completed state of their being in good condition, or to put it more simply (to come all the way back around to my first point), their "good condition."
Perhaps an even simpler way of understanding this is to view it this way: Just say that the direct object (phrase) of the verb "find" is toilets in good condition. Simple as pie.