I'll try the first one, sounds easier.
The second.. the physical connection would loop be?... input 3 L into the pedal then out of pedal into output 3 L?
Then in the grid?.... a empty block with input 3above, output 3 below?
Output 3 L into pedal, then pedal out into Input 3 L (or connect in stereo for stereo effects)
Grid might be something like:
IN1 ->
[stuff] -> OUT3 -> IN3 ->
[other stuff] -> OUT1
Bypassing IN3 (or any IN block) will cause it to function like a shunt. When an IN block is active, it discards signal at the grid input, so by having OUT3 connected directly into IN3 on the grid like that, when IN3 is bypassed your grid signal will flow directly from OUT3 to
"other stuff" as if the IN3 block weren't there, but a shunt was instead. However, when you then activate IN3, the connection between OUT3 and IN3 on the grid is ignored by IN3, so your signal goes from "stuff" out to your external gear via the Output 3 ports on the back of the III, comes back into the III from your external gear via Input 3 connections on the back, and then IN3 passes that signal onto
"other stuff" without ever seeing the signal at the connection between OUT3 and itself.
FWIW, Page 30 of the manual has a nice writeup and example with additional pictures and labels on that kind of setup... worth checking out if you ever want to experiment with routing parts of your grid into additional effects units before being processed by other parts of the grid in the III.