The two assassins are found at a drain pipe large enough for people to go through. So they evidently entered the compound through that pipe, or at the very least it served as their escape route.
But it no doubt dumped into the lake. To where would they be escaping?
I guess a boat was waiting at the spot were it dumped into the lake. Perhaps the assassins had to swim for a few metres. Not unbelievable imo. Anyway, it is clear for the viewer that they were to escape through that drain pipe.
