Phantom leak - Zodiac Yachtline

[Lemmy]

Folks - appreciate your advice.
I have a 4.9m Zodiac Yachtline - made in 2001 - with PVC tubes.
Because it's been meticulously looked after - it's still going well and has the original tubes.
But - it appears to have a hull leak somewhere.
Every time I take it out after a session, a massive amount of water comes out of the bung hole when I release it.
While on the water, I run a bilge pump which alleviates the problem - but if I don't run the pump I end up carrying around half of Sydney harbour.
I've checked the hull carefully while on the trailer, (focusing particularly on hairline keel cracks which might open under load) but can't find any obvious cracks or holes.
Any advice as to other methods to identify where the leak is coming from?

[Iankristy]

While on the the trailer fill with water. See where it come out?

[cgoing]

Remove the tubes and inspect the track carefully. Sometimes they separate at the back ends causing leaks into the hull.
Recently repaired a zodiac pro that had that issue.