Wow great advice. I butchered the holes with a drill and a wood hole drill bit and pressure to make the holes bigger slowly.
If they're still leaking after this I'll have to go get new buckets.
Yeah, first time I just went for it as fast as I could. Loads of pressure and had the speed cranked up to get the job done ASAP. Regretted it! I examined the buckets to find the leaking points and then took it all apart... found the tiny gouges. With rubber grommets they need to be perfect. I haven't read anyone explain that on any guide or forum but it's important for your sanity! You can't trust the grommets to fill out any irregularities.
Here's what my holes looked like in the end with flat wood drill bits, slow speed and light pressure:
If you're using bulkhead fittings you can drill any old wonky hole and they'll be leak free. You see some pictures of the shitty holes people have made for their RDWC and think WTF how is that not leaking?!
Also get into the habit of using a ratchet pipe cutter to cut all your hose/pipes. They make clean cuts which are less likely to leak.