Council of Elrond

Longbottom Leaf :

"Take up to two resources from your sideboard to your play deck and reshuffle. Remove this card from the game."

Pipe :

"Unless bearer is an Elf he may tap during the end-of- turn phase and make a corruption check to bring one Longbottom Leaf, Old Toby, Pipe Weed or Smoke Rings from your discard pile to your play deck and shuffle. If bearer is Gandalf or Saruman, you may take one of these cards to your hand instead."

When played, Longbottom Leaf is removed from the game, not discarded. So, it is normally not possible to use Pipe to bring back it from the discard pile to the deck...

Correct, normally. But you can still discard it by a lot of reasons (Khamul, because you want at the end of turn, you put it on guard and your opponent sends it packing to Mordor...).

or back in straight to SB and bring 3 & 2 Smoke rings to discard pile by tapping an avatar

Vastor Peredhil wrote:or back in straight to SB and bring 3 & 2 Smoke rings to discard pile by tapping an avatar

Probably the most common situation...