In reply to Timmd:
If you go down the PLA route, it's worth considering it will hydrolyse, and therefore degrade, over time, with exposure to food, and more importantly hot washing up water. This will release lactic acid, but (disclaimer, don't take my word on this) this shouldn't be too much of a toxicity concern. * *PLA is made using tin catalysts, however, and if your 'pusher' breaks down over time, you run the risk of ingesting some pretty nasty tin compounds (not to be recommended).* *
The other consideration is the tacticity of the polymer. Presumably 3-D printing filament will be fairly isotactic poly-L-lactic acid, which is good up to c.180 degrees C in terms of melting, but the glass transition temperature is much lower, so it would run the risk of going floppy and losing shape, depending how hot you washed it.
I reckon if it was me I'd stick to either wood, or a food-grade non-compostable plastic.