Usually, I drain ‘Subungal haemotomas’ (woohoo! new medical term) by drilling through them with a pin vice and a teeny tiny drill bit. Make sure you do it when your nail’s hard (not after a bath) otherwise it won’t drill properly - it’ll ‘corkscrew’ in and hurt like hell.
Drilling down works too, but we normally use 21Ga needles at work, because no one ever seems to have a candle or a paperclip. Just very gentle pressure and patience required. The holes don’t come out quite as big as a red-hot paperclip, so you have to drill quite a few holes to evacuate the haematoma.
You could try a soldering iron too.
The trick is not to put too much pressure down- you’ll pop through the nail and the blood will come out long before you hit your toe with a red hot paperclip or a needle.
Thanks for the tip. I have them under control now (using benzoyl peroxide) but there’s one around the bike shorts cuff line that’s really deep and I’m thinking I’ll have to go to the doctor to check it out.