I drain the tank. Run an airline into the fuel tank from my air compressor with the regulator set at a couple PSI and let it run for a couple days, so there's always fresh air circulating into the tank. Give it a whiff, any sign of fuel presence? If so, give it a couple more days, if not then box it up and ship it. Like @OMC , my first concern is that it's actually safe to ship. Beyond that, I'm only slightly concerned with following the actual letter of the rules. When the USPS clerk asks me if my package contains anything flammable, explosive, etc. I can very truthfully say no. I shipped a chainsaw via UPS and even though they weren't as picky, I still followed this procedure. The penultimate paragraph on the poster OMC posts does give me pause.
After cleaning, leave the fuel cap off the tank and ship both in the same box. Explosive gas can't build up in an open tank. Ben
Just picked up a stove at the local postoffice here in Norway. Just entered the store/postaloffice when the staff told me that there was a parcel waiting for me. And that there was a leak and they though it smelled gasoline. Not a good way to start the day. When I reached the postalpart of the stove I figured they were right. The whole dep. smelled of kerosene. No comments other than that they made a note of breakage of the parcel. A bit embarrased of the situation. So; clean an drain, and drain and drain. If I send a stove it's always labeled as "old/vintage camping gear" and I send it empty.
"Try one rinse with acetone instead. Gasoline is not miscible in denatured alcohol but it is in acetone. Acetone also evaporates quickly cutting down on the drying time." Alcohol will actually mix with gasoline. Think of carburetor spirit.
