Can I change the default trash sounds? I'd love to change the default empty trash / move to trash sounds. I found this on Github, which is a script to change a bunch of defaults. The default alert is mentioned, but nothing about the trash.  

Alternately, this other AskDifferent question discusses how to add a custom alert sound. Does anyone know the path to where the trash sounds are stored? Could I just replace the sound file as in the linked SO thread?
You would need to change *.aif sounds in:

 /System/Library/Components/CoreAudio.component/Contents/SharedSupport/SystemSounds/finder


There are:
empty trash.aif and move to trash.aif (self explanatory). I recomend to make backup of those files before swap.