I own steel tanks (1 air and 2 using banked NITROX) and recently had all 3 of them hydro tested. My LDS did a quick visual before taking the tanks to the hydro facility an hour's drive away.
After he picked them up he tumbled each tank to get any flash rust or gunk out. He then did another VIS, remounted the valves with new O rings, stickered and filled the tanks O2 compatible air (they sell banked Nitrox 32 - no PP fills). This was all included in the price of $40.00 per tank which I felt was fair.
NOTE: I did have to pay for 2 new NITROX tank bands to replace those removed for the hydro which I expected.
After he picked them up he tumbled each tank to get any flash rust or gunk out. He then did another VIS, remounted the valves with new O rings, stickered and filled the tanks O2 compatible air (they sell banked Nitrox 32 - no PP fills). This was all included in the price of $40.00 per tank which I felt was fair.
NOTE: I did have to pay for 2 new NITROX tank bands to replace those removed for the hydro which I expected.