Rss farming is something that we all do, but from time to time you can get lucky and find some large abandoned bases.
A good sign is that there are no troops left, and that the base has lost its tags. Lost tags means it is no longer member of any alliance.
These opportunities are a bit rare but if you find them, share them with your alliance, because no matter how big you are, you will never be able to emptying it alone so invite the rest of your alliance. An example of a big abandon base below.