3" corrugated plastic duct from new building to other outhouse,
intended to pull service cable through. Total length about 25 metres.
Currently blocked 18" from one end just round the bend. It goes
vertically down into the concrete slab, then bends horizontally and
out to the other building. Ducting has tracer pull though of thin
steel wire which will not budge. Frustratingly it was possible to push
a cable snake from the blocked end before the renderers did the wall
so I'm suspecting a blob of render has gone done despite the end being
taped. Short of breaking up the slab any suggestions to clear it?

AWEM