Base to stop plant pots dripping water.

Sizes to suit a couple of small plant pots are available, and OpenSCAD source so you can make whatever size you need. Size the base 5mm-10mm larger than your plant pot base.

I have just used these to stop drips, I do not fully flood them with standing water.

Some 3D printers might not print fully waterproof.

If you want to leave standing water in yours, then I would give them a couple of coats of epoxy glue, just mix up the 5-minute epoxy and apply with a paintbrush. That would make it reliably waterproof.