Got curious and found this ~38 minute video:

Includes some specialized tools to make a quick-connect and fitting, but there might be work-arounds and/or places to rent them.

21:39 there's great info on zip-tying so lines don't rub against each other.

Mentions using 3/8" steel truck air line around and plumbing compression fittings at 35:25 or so.

Edit: remember that Avalon is a Camry. You might ask your question in whichever Camry forum for your year Avalon.

 

Replacing gas lines

Thank you for getting back. The gas leak is in front of the under casing of the tubes towards the front of the car..
The tubes are rusted and leaking underneath the cover going to the front of the vehicle. We have already had the brake lines replaced and they are outside of the under casing. So the only 2 lines that are running under the plastic casing that is running to the front are the 2 fuel lines. So can I run a new fuel line and return line from the back to the front lines coming from the engine with steel pipe /tube and with compression fittings? They would be outside by passing the plastic protective runner.
What would be the proper metal tubing size that is needed for this job?
What size compression fittings would we need?
Is there any thread that has detail instructions for this type of installation?

Would appreciate any help with this.
Thank you, melw

 

The details I don't know, as I haven't done it. The video suggests 2 materials - nylon fuel line from a (large) auto parts store or steel tubing.

I'd be hesitant to run a nylon gas line on an un-armored run. The video mentions 3/8" tubing for both nylon and steel. In our area, the guys at Home Depot would be able to tell me which compression fittings to use with what steel line.

Since the Camry:Avalon ratio is about 100:1, someone in the Camry forums might have done a fuel line replacement...

 

Thank you for the come back.
But I need the location of where to find in the forum regarding a replacement of the fuel line.
in detail please

melw

 

If you mean the TN forum that corresponds to your 1999 Avalon, probably this one: https://www.toyotanation.com/forum/...n.com/forum/103-camry-3rd-4th-gen-1992-1996-1997-2001-1st-gen-solara-1999-2003/

If you mean, how do you search out relevant posts, I suggest NOT using the "Google Custom Search" at the upper right, though it's pretty good. More comprehensive searches come from an external Google "site search" something like the following: replace fuel line site:https://www.toyotanation.com/forum/...n.com/forum/103-camry-3rd-4th-gen-1992-1996-1997-2001-1st-gen-solara-1999-2003/

You can search all of TN the same way: replace fuel line site:https://www.toyotanation.com

I just tried the second one - lots of hits, but of course they are for EVERY vehicle made by Toyota across all time periods in TN.