So I slowly ran the tube through the kitchen sink 5 times, and couldn't see any air bubbles.
Tried holding the valve under for about 30 seconds too, and nothing.
It's a second-hand bike. I know this because of the dirt on the tube (not my bike, just doing a favour), but there are no patches on the tube, so that's obviously new.
Anyone know what the craic is here.
The valve is one of the really skinny ones.
How much pressure did you have in the tube when you held it under?
Buy a new tube for a fiver...
Buy a new tube, but if you can’t see bubbles you are either not squeezing it. Or it the nozzle , put it under abs the move
This maybe? I haven't had this in 20 odd years though and it was my Dad's bike back then when it happened.
How quickly is it going down? I've always found even the slowest punctures can be found by holding the tube under water - including air leaking from the valve. I usually use a basin and make sure it's in good light. For very slow punctures it might take a couple of rounds - slide your hand along the tube while underwater to clear away any air bubbles sticking to it, then hold each section under for a few seconds. Also try inflating it a bit more
Yeah, make sure to stick the valve under the water too, as said. You could try inflating the tube a bit more, as also said, as some small punctures remain closed at low pressure.