Well, I can finally post a bit from experience here.
After reading this thread the first time, I went out and bought two of the flat "backwash" or "discharge" hoses.
One from Lowes. One from Harbor Freight.
The one from Lowes cost half of what the one from Harbor freight did, and was twice as long. (L = 50', HF = 25')
But... The one from HF is TOUGH !!!!!! The one from Lowes is pretty wimpy.
I bought these to use for their intended purpose. Discharge hose.
And did use them for that.
With the very least bit of restriction on the end of the Lowes hose.... It exploded. It's only about 3 times as thick as your average party balloon.
The HF seems to be as strong, as solid plumbing. It certainly held up to a huge amount of pressure. Even when completely capped off, it held.
This is a pump that can empty a 55 gallon barrel of water in less than a minute. Put a garden hose on the end of the discharge hose, and the water sprays 50 feet and more. That's a LOT of pressure.
So my vote goes to the harbor freight hose. (The package says max pressure 58PSI, but it had to have stood up to three times that, at least.)
The item number for the hose is 95391. It's called PVC Discharge Hose.
I would suggest installing it by first stuffing it in the tire, flat, and marking it with about a 5 inch overlap.
Make sure it's tight into the tire. You'll be less likely to leave any gaps, later.
Once cut to that length, cut 5 inches, (or whatever your overlap was), from only one side of the hose. (Refer to picture attached.)
Cut the 5 inch piece out of -opposite sides-, on both ends of the hose.
Then, install in the tire with whatever glue you decide, making sure that the two ends overlap each other.
I hope the instructions and picture are clear enough.
If you do this right, you will have no gaps, and no overlap bulges.