I haven't been asked to submit a full manuscript yet, but I'm guessing that people who have submitted them mail them in a box? In that case, it'd be impossible to send a self-addressed stamped box (SASB?) to get the thing back, right?
You can by manuscript boxes at Staples. I bind the pages with one large rubber band, but never use staples or paper clips. As for return postage, I always add on the cover letter that the pages are recyclable (I have a laser printer, so running off a copy for me basically costs the price of a pack of paper).
So if you don't expect to get it back, then how does the agent dispense editorial advice? I've read about people getting suggestions after submitting their work. Do agents email something like 'on pg. 72 there's this, on pg. 106...'?
Agents rarely offer editorial services unless they are willing to sign you (or think they can guide you to a point in which they'll offer representation). They just don't have the time, and it's not their job. Even if you're a client, not all agents will do line edits with you. It just depends.
Personal experience: I sent an agent a full manuscript, as requested. It had an SASE for reply, but I didn't expect the actual pages back. She emailed me back a few months later, saying she wasn't offering, but there were changes she'd like to see in the manuscript. She wrote two or three paragraphs of thoughts, and said if I agreed with those changes, she'd be interested in reading another draft.
Or maybe line edits are only for clients? That's another question I have. How do clients work with agents and /or editors once their book has been sold? Do agents /editors give authors a hard copy with changes to make? Or even before it sells, there must still be hard copies with edits somehow going between author and agent?
Many agents will do this work via email and .doc attachments. My agent received the hard copy, but everything else we've done since has been via digital copy. From what I've read, too, many editors will use attachments. It's faster, more convenient, and cheaper.
Again, personal experience: So far, I've done two rounds of edits with my agent (not the one mentioned above, different agent and different book). The first one came in the form of an email. He had several paragraphs of specific plot elements, characters, and backstory that either needed changing, adding, altering, tailoring, etc.... That edit was up to me. I sent it. A week later (yeah, he's fast!), I got it back with line edits and comments set in .doc track changes (I love this feature!). Again, I went through and implemented the changes, and again, it went back as an attachment.