I’ve done this mod before, just getting to it now on my T4R, since my parts came in.
Some people think/say it is unnecessary, and that’s their opinion which I respect. Some people that haven’t done it, in hindsight, wish they would have.
We have referred to it as the “Scuba Mod” (reference Toyota FJ Cruiser Forum - View Single Post - Saker's 2013 TT/SE Build) and I did it on my FJ Cruiser.
This one being done is just slightly different because of how it is routed and configuration of the bottle jack compartment. I used @hoeftm2002 ’s example in his post: New Location for Rear Diff Breather Ext.
Cut the hole with a hole punch in rubber plug # 90950-01958, inserted fuel line, routed it, removed OEM one-way valve from differential, installed the 90404-51026 Toyota 1/4" Fuel Line Union, left enough slack in fuel line for rear end flex and installed line to union with clamp. Cut fuel line at bottle jack compartment to correct length, installed line to 1/4 X 1/8 HB Male Adapter with clamp, installed the bracket to bottle jack compartment. Done!
Photos included with descriptions below.
Parts used:
(1) 90404-51026 Toyota 1/4" Fuel Line Union (Cost: 6.00)
(1) 1/4 X 1/8 HB Male Adapter (1/4" Hose ID X 1/8" Male NPTF Adapter)
(1) FJNewb 2 Port Manifold with Filter (Cost: 30.00 Shipped) Just the Manifold/filter can be purchased!
Link:Differential Breather Kit - Raw Mind Engineering
(1) 1/8" Brass Pipe Plug (Already had)
6' of 1/4" Fuel Line (Already had)
Hose Clamps to fit. (Already had)
Aluminum Bracket fabricated: I made mine out of a piece of 1/8" thick aluminum cut to size, bead blasted, marked & drilled the holes. (Already had)
I used brass machine screws, washers (flat and lock) and nuts to attach manifold to bracket. (Already had)

Scuba Manifold w Bracket


Differential Nipple


Diff Check Vv


Hole in Plug cut w 1/2" Tubing


Hose & Plug Attached


Hose Routed


Hose Routed On Fuel Fill Line


Nipple Installed w Fuel Line


Flexed And Still Slack In Line


Scuba Maniflod Mounted In Jack Compartment