Where to fill air in dually rear wheels?

Although I don't have a DRW truck, I carry a small compressor and could easily add the necessary tire chuck needed for DRWs. The small compressors come in three categories, ****, fair and good. Get a good one and you will be fine! The good ones will clip to your vehicle's battery (the engine must be running)(some can be permanently mounted and hard wired) they will set you back $150 or more. I have the VIAIR 400P Automatic which I got for $175 and it works great and can bring my truck's tires from 65psi to 80psi in only a couple of minutes. Don't go cheap! We had a tent trailer that we would air down from 50psi to 30 psi when camping in remote areas. The cigarette lighter compressor we had would take about 15 minutes per tire when airing back up and everyone for a mile around could hear it struggling. Having an air compressor along is very convenient, compact and light weight!