10 liter fermentation crock... water getting sucked inside, advice needed
Is the crock kept in a place where the temperature is steady (such as a cellar/basement) or is it exposed to daily temperature swings? As a a rule the ferment should produce gas to some extent (which would push water out, if anything) but repeated temperature swings would tend to "pump" out when warm, in when colder. When the initial gas production slacks off, that could lead to water pumping in, particularly with a defectively non-tradtional design as you describe (I have looked at fermentation crocks a lot, and so far refused to spend money on them - but I soon grasped that the entire contents of the "moat" should not be able to rise above the inner lip in a "suck" situation, for precisely the reason you have experienced.)

One option would be to go back to a very basic airlock - a sheet of plastic wrap, or a (food grade) plastic bag, that covers the top of the crock, and a large rubber band holding it in place. 

Another would be to NOT fill the moat - put just a bit of water in so it seals, but not so much that suck-back would pull it over the inner lip.