I also vote for muriatic acid, it works great on concrete.

It also rusts steel.

i
On 2011-06-13, Larry Jaques wrote:
On Sun, 12 Jun 2011 09:22:19 -0700, "Steve B"
wrote:

How do I get the residual concrete to release from my yard sale concrete
tamper? One of those two handled things with the 8" x 3' bottom screen.
Probably paid too much for it ............... $10. Spray with vinegar
water?

Straight vinegar would probably work. But for $5 at the pool store,
you can get a gallon of muriatic acid which works instantly. Dilute it
by pouring an ounce into ten ounces of water. Pour on, wait a few, and
the concrete slides off. Neutralize with baking powder


Soak overnight in plain water?

That'll rust the portion which isn't covered in cement.


Spray with some sort of petroleum
product like WD-40 and let soak overnight.

NO.


Then hit with power washer? Or just power wash?

A brush and water, wipe or air-dry, and oil 'er up.