How about this? Buy an external drive case with a SATA internal connection (to plug in the SATA drives) and an eSATA external connection to the computer. It will have its own power supply module and should have an on / off switch. Even if you don't have a computer with an eSATA port, many of these cases come with a simple adapter bracket that plugs into an internal normal SATA port and converts its connection to an eSATA port.
Now, open up the new case and leave it open. Plug in one SATA HDD. Power up the unit and it should show up in My Computer. Now use a software utility to wipe that drive. When done, use the Remove External Hardware icon at lower right to remove this eSATA drive, then turn off its power. Swap out the wiped unit for another. Power up and repeat the process.
For "wiping", how good does it have to be? Deleting all Partitions and then re-Partitioning a disk and Formatting it will foil amateurs. The original data still exist but it takes knowledge and skill to do it. Zero-filling it entirely will destroy all the data, but a really well-equipped shop could recover it from the weak "echoes" of it on the magnetic surfaces. A military-level wipe system makes multiple passes over the entire disk, each time writing a specific bit pattern designed to destroy previous weak echo patterns. This latter process is virtually impossible to defeat, but it takes a VERY long time per unit. (Makes the hammer technique look attractive!)