Adding fiting to air up truck

Hook right into the stainless steel braided line coming off the air compressor?

 

Does truck have glad hands if so get a airline hooked up to red glad hand and push button in least you can do that on most trucks..my current truck has a air fitting on air tank that way tanks can be drained in shop to get rid of moisture then refilled with shop air so truck doesn’t have to run in shop to pull it out in winter.

 

We always just screw quick couplers into the air tank just like you would see on your shop air to where you can plug your line in and air up a tire. Then if you want to air up the truck with shop air or a portable air compressor. That hose usually has a quick coupler at the end of it so use 2 male style M's screwed together to connect the Female on the truck and the female at the end of your air hose.

Homedepot carries them. We use Milton style M on everything that has air. All of our air tools, blower nozzle's on every truck, in the shop. EVERYTHING!

I think you have to put it in the primary tank if you want all tanks to air up.
Usually there is a plug somewhere in the air tank.
If there is no plug to remove you have to buy a 1/4 inch Tee to tap it in somewhere.
Milton Industries, Inc. 1/4 in. MNPT M Style Coupler-S-716 - The Home Depot

And these will screw strait onto your 1/4 inch air line.
Husky 1/4 in. NPT IM Brass Female Plug-HDB21800AV - The Home Depot

One time we brought the Lowboy in with a failed air compressor by keeping the system aired up with a gas engine powered air compressor.

 

I once was losing a great deal of air but never could find it. Turns out it was the main line going from the compressor to the dryer 1st. That line would empty out immediately after shutting the truck down so there was nothing to listen for.

Airing up the tanks did nothing because of a check valve I guess at the dryer. I had to disconnect that line from the dryer and put shop air on it before I could find the leak. Turns out it was inside a heat shield where it crossed from right to left across the bell housing and transmission.

Where did you find the air leak Glenn West if you don't mind me asking?

 

What is that like a supply line that keeps air pressure fed to the bag?
What size is that line? I would think at least a 3/8".