Simultaneous giving and receiving definitely can put me in The Zone.  Almost an out of body experience.
 
And yes, the rectum -- if very clean -- smells and tastes great.  In fact, the deeper your tongue goes the sweeter it gets!
 
But, she must have a nice butt, a nice starfish, and be VERY CLEAN.  (Vegetarians taste best too!)
 
Long ago I discovered the key to getting as clean as possible for ass play:
 
The STREEMMASTER.
Here's one good link for it:
http://rebelsnotes.com/2013/07/produ...shower-douche/
 
Very easy to use.  Hangs on the shower head.  Water is gravity fed, so it's high volume but low pressure; perfect for the rectum.
 
Start with a little soap on the outside of your starfish (cleans and lubes), slip in the nozzle a few inches, let your rectum fill with water, expel it out.  Repeat, perhaps 5-10 times, until the water streaming from your butt looks and smells like the water coming from your tap.
 
The repeated filling and expelling has two effects: 
1- Cleans your rectum thoroughly enough for deep tongue fun, without soaping your insides.  Too much soap will irritate the rectum.
2- Will likely stimulate a bowel movement, if you're close to having one anyway, which then of course has the added benefit of leaving you empty, which is always a good way to be for sex.
 
In fact, I use it daily, often right after a bowel movement in order to complete the job and get it all clean, or sometimes I'll use it when I need to go but can't.
 
Get one and enjoy!