I can see the funny side of helpful forum members telling a retired medic where he can get tongue depressors from (thanks, guys, the links are helpful), but I probably didn't make myself clear. In my day the supply cupboard doors opened easily and in such a way that said TDs fell out into my bag rather faster than I used them to inspect tonsils, so that there was scope for lateral thinking such as epoxy mixing and filleting. These days I am sure some sort of dragon keeps the key to the cupboard. Anyway, to quote W S Gilbert, " I am now a respectable chap, and shine with a virtue resplendent" (Trial by Jury), and wouldn't dream of such behaviour in this age of cost-cutting, even if I was still in harness: hem-HEM. I was, of course referring to the intra-NHS situation, and was aware that most medical kit (operating theatres, glass eyes, the lot) is available on the internet if you know where to look.
It may have been noticed that I sometimes ask a question and then sort out the answer myself. So it is, probably, with hole filling. The point is to make sure the hole is watertight and then achieve a flat surface for finishing. I'm sure it doesn't matter, structurally or otherwise, if the hole (most holes, anyway) isn't full of epoxy right to the bottom. The problem with a runny mix (which you would need if you tried to use a small syringe, Anthony) is that an air bubble is usually trapped, it looks OK, and then when it cures you've got a dimple because the air worked to the top and the remaining epoxy sagged into the hole. I'm sure Simon's approach is right, using the micro-ballon filler and a reasonably stiff mix, and leaving a blob over the hole to sand smooth.
Incidentally, something else which has changed since I was actually building (in 2004) is the range of fillers now available. At that time, 'easy sanding' in the context of epoxy was definitely an oxymoron, and I'm looking forward to a somewhat easier life in that respect this time round.
I have to say that, since Simon's initial reply to my first post, I continue to be mildly gob-smacked by his idea of sheathing panels before assembling the hull. It seems to make every kind of sense - doesn't it? Anyone else got any comments? Am I being completely naive in finding it so brilliant? Does everyone do it? Anyway, I shall certainly do the same when the time comes, unless other builders have cautionary tales advising against.
Anthony, you haven't told us which boat you are building. It's a great experience, enjoy!