[downrightmike]

Why not try a large Stanley cup? Double layered, top seals shut, pretty easy to get a hold of.

[zikduruqe]

Your microwave oven is pretty good at attenuating 2.45 GHz signals.

[wiml]

That's a notch filter, though. Attenuation outside of whatever stopband the microwave door was designed for won't be nearly as good.

[zikduruqe]

Very true.