I have seen the same situation with my A122, however it never overflowed the drainer.
So this sounds silly .. but i stuck a small branch to compress the clear hose drains from the top, and voila ... it drains ...
Now ... i must admit, im a bit of a nut for leveling things .. both back/front and side to side, but compression of the clear hoses works for me ...
im thinking the problem could be simply a air lock issue ...
2008 Nissan Frontier 4x4
2011 Rockwood A122