So after some research in other threads for older Toyotas and some help from a couple of members, I finally completed my differential breather extension. This mod extends the differential breather to a location behind the driver side tail light.
Why do we need to extend our differential breather? Well, we don't NEED to, but it is a good idea to do it. So why is it a good idea? Extending the breather to a higher location prevents the differential from getting water and mud in it due to negative pressure or stock breather failure. This mod extends the breather to a higher location so that you can go through mud and water and not worry about destroying your rear end due to mud and water entering the differential housing. You know how high the water can get before you have to worry. If water gets as high as my new breather hose end, I have more to worry about than the rear differential.
So here is a list of what you need for the job. The cost for everything was about $23. You can do it cheaper if you search for better prices. Anything without a price on it was already in my possession.
T30 Torx screw driver
Socket wrench
14mm deep socket
12mm deep socket
Toyota Union - 3/8" (Toyota part #90404-51319) -
about $7.95 from dealer
10 feet of 3/8" fuel line (I used 7 feet for a CM, so add length depending on your bed) -
$0.99 per linear foot
#2 Phillips screw driver or #2 flat head screw driver, either is fine
3 x metal pipe clamps (bottom left of picture) -
$0.69 each
3/8" barbed inline fuel filter (any will work, I used a NAPA Gold 3003 since I was getting the fuel line there) -
$3.99
5 x zip ties (you might want to use more)
Teflon thread sealing tape (not pictured here)
Screw gun/drill (not necessary, but makes the work faster
small piece of screen (keeps bugs out of the tube)
6 pack of cold beer (this is optional and liquor can be substituted), you will probably only need 3 or 4 of them. -
about $5.99 
Here is a picture of the stock breather from the driver rear corner of the truck. It's the silver nub in the center of the picture.
Crack open a beer and drink at your own leisure.
Here's a picture of the tail light with the tailgate down. You need to remove the screws at the top and the bottom of the picture with the T30 Torx head screw driver. If you don't have one of those then you should stop and go get one now.
Here is a
PDF file from the manual that shows how to remove the tail lights if you need it.
Once those two screws are removed, get your fingers around the edge of the tail light and pull toward the side of the truck. There are two friction tabs holding the light in place. Here's the back side of the light. You can see the black tab at the top right and the silver tab on the right of the picture. This should give you and idea of their location.
You can unplug it all and remove the light if you want, there is a plug under the truck you can unplug if you want an easier way to take it out. I just turned it around and hung it down on the side of the truck.
Now climb back under the truck and keep your tools close by on the ground.
First you need to remove the stock differential breather. Use the 14 mm deep socket wrench. A crescent wrench will work too. The little silver thing in the middle is what you are removing.
You will hear some air moving into the differential when you remove the stock breather. This is fine and means the old breather was working as it was designed to. It lets pressure out, but not in. You want the breather to allow air both ways and the new one will.
Here's a picture of the Union on the left and the stock breather on the right. Their corresponding deep sockets are beside them. Use it for size reference. You will not be using the stock breather anymore. Do whatever you want with it.
Take the teflon tape and wrap the threads on the union twice. Most of it will come off since it's already a snug fit, but it's still a good idea to put it.
Carefully hand screw the union into the differential. Be careful while doing this and make sure it is going in straight. You don't want to cross thread it. It should go in a few turns before you need the wrench. Tighten the union down. I just stopped when the treads were no longer visible and it felt a little snug.
Now run the clamp over the 3/8" fuel line you purchased and push the fuel line onto the union. Don't forget to put the clamp over the tube first. The tube should go on with a little force. Then use the screw driver (or screw gun) to tighten the clamp over the hose. The clamp isn't absolutely necessary since the tube won't be pressurized, but it's better to have it there.
You could probably use another beer by now. Maybe not. Just a reminder in case you do.
Now run the hose between the truck bed and the frame so it will be out of the way. You need to leave some slack at the differential for axle travel. Look at the other hoses going to the axle and kinda match the length.
Run the tube where it is out of the way. I went above the frame and found some holes to use for the zip ties. Here a picture of one of the zip ties. This is above the driver's corner of the spare tire. The tube runs almost straight down the center of the picture above the frame work. You can see the tube at the top and bottom of the picture.
Here's another spot where I zip tied the tube. This is next to the tail light under the truck. The tail light is in the bottom right of the picture. Don't make this too tight or you'll crush the breather tube. It's OK to crush it a little, but not too much. Just zip tie whatever you think will need it. Use two at a time if you want since zip ties have been known to break. That's part of the reason I didn't use the tiny zip ties.
So continue this and run the hose up to the tail light location. Now you should be done under the truck. Clean up your tools under there and you can do the rest standing up.
From above, I went ahead and put a tip tie to attach the hose to the tail light wiring loom since the loom if secured to the truck just before it goes up to the light location.
Run the hose up the tail light opening and find a place where you want to place the fuel filter. You want the fuel filter to be either in-line or at the end of the hose. I decided to do mine in-line. See how much hose you need to the filter location and cut the extra off. I'd suggest pointing the end of the hose down. Just in case the water does get that high on the truck, you don't want water just flowing down the tube. If the end of the tube points down, then it will still keep the water out. Hopefully it's a very rare occasion that the water gets that high. Only time I could think of water getting that high is if there is an accident at a boat ramp.
Anyway, put a clamp on the hose and be careful to make sure the clamp doesn't slide down the tube and under the truck. Now put on the fuel filter. I got the clear plastic filter just so I can check it if needed. Use the clamp to secure the hose to the filter. No need to go too tight since it's not under pressure and the filter is plastic.
Loosely secure it in place with a zip tie.
The black thing on the right is the hydrolic for the tailgate. Here's a better view of it:
Attach the extra hose and use a clamp to secure it.
Zip tie the filter in place so that it is secure. The location where I installed mine allows the filter to be secured with a zip tie above and below it. Put the small piece of screen over the end of the tube and use a zip tie to hold it in place. This just keeps bugs and spiders from crawling in.
You can trim the ends just to keep it looking good.
I did notice some spider webs where the hose is so this should keep any spider, bugs, mud dobbers, or whatever from making that a new home.
Now put a curve in the tube and point the end of the tube down. Zip tie in place and step back. Have another beer while admiring your work.
Replace the tail light and everything looks stock from the outside. You are done and can have a couple more beers if you want.
Thanks to all those who have done this before me on other trucks and posted their write-up and pics. And thanks to Squid for hosting it here on TundraTruckz.com.