Drainage Solution for Alloy Tray with Bottomless Canopy

I've got an aluminium, bottomless canopy mounted on an alloy tray. I'm thinking of drilling a drainage hole in one of the tray corners—would using a bathroom plug be a good solution? The smallest plug I can find is 25mm, but my drill set only goes up to 10mm. Would a smaller hole with a blanking grommet work instead? Appreciate any advice. Cheers!