According to HeyBub :

We used the Bic Lighter technique for checking.

The soapy water technique is MUCH more sensitive to slow leaks, and
is why the pros use it. A leak could be too slow to ignite
with a lighter - mixes with too much air before it hits
the lighter. But a slow leak can get worse, or, accumulate
gas in an enclosed space after you've buttoned it up.

I suggest you retest it ;-)
--
Chris Lewis,

Age and Treachery will Triumph over Youth and Skill
It's not just anyone who gets a Starship Cruiser class named after them.