I use a 1mm drill bit and do about 16 - 24 holes for a 2.5 or 5 litre bucket. If you stack the lids up tightly you can go through several at a time.
The secret to use is to not fill to the top, hold bucket lid up, squeeze top to bottom to push some air out, and whilst holding the squeeze (as it were) turn the bucket upside down and relax. The vacuum holds the syrup back, but clearly you want a secure lid!
For a really small feeder, many suppliers offer "Jar Attachment Feeders" - a plastic lid with gauze insert that fits a standard 1lb glass jar.
For less than £2 each, and no flood risk, I've invested in a couple.
Only real snag is not being quite big enough to completely cover one of those damn Porter holes. A slip of plastic makes a flange to cover the Porter hole without much bother.
Although I do have smaller-sized drills, I often use a 1mm drill-bit in a standard-sized pistol-grip electric drill - but - you need to have very steady hands (!) and be prepared to lose one or two.
Drilling such holes in plastic or thin metal jar-lids does not present a problem - just tap a sharp nail into the surface to be drilled first, to prevent 'skidding' - the most common cause of such small drill-bit breakage.
ToolStation currently have 3/64" drill-bits on special (clearance) offer - £0.57 for 10 - they're a bit on the small size for building-site gorillas - but are ideal for drilling feeder holes. I've already stocked-up with 'em - so, "g'arn, fill yer boots".