I just picked up my tank last wednesday after having it hydro tested. I paid $34. That included a visual inspection prior to the hydro, the hydro test and an air fill. Normally the visual is $8 and airfill is $4 so that means they are charging me $22 for the hydro test. The $40 they were trying to charge is a ripoff and I'd be complaining too. I have used my tank for many things for years as well as diving. There's nothing illegal about using a tank for other purposes. I got a used regulator that my instructor/technician wasn't willing to pass for scuba use and I use it for a portable air source all the time. It works great for an air source for my airbrush as the air is completely dry and lasts forever for painting. When I was racing dirt late models I could mount and fill 8 tires from a single tank and these were pretty big tires. I carry my tank with me whenever we use the motorhome or take the boat out as a slow leak could be topped off every so often till I could get the tire fixed properly. The uses are endless. One issue however is that noone should be able to get an airfill unless they show a dive certification card. Filling a tank for an uncertified person is illegal even if they aren't using it for diving.
Later,,,basmntdweller