Leak at plastic soil pipe to clay soil pipe join

I have a leak at the join between the plastic soil pipe running vertically down from the bathroom and the clay soil pipe sticking vertically out of the ground. They are connected by a HepSleve plastic connector.
On inspection (throught rodding eye) the plastic soil pipe stops 10mm short of (i.e. it doesn't fit into) the clay pipe, as I would have expected. Therefore the join is relying on the seal between the OD of the pipes and the ID of the plastic joining sleeve that both pipes fit into. The leak is between the clay pipe OD and the joining sleeve ID.
Is this normal, or should the plastic pipe go slightly into the clay pipe?
If so, unfortunatly, dropping/replacing with a longer plastic pipe is not really an option. Major distruction to bathroom tiles would be required.
Any ideas?
Many thanks,
Darren
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It is possible that the soil to clay adaptor has moved or been damaged. There is an application detail drawing showing how the connection should look here: -
http://www.hepworthdrainage.co.uk/pdf/technical_manual/application_application_details_2.pdf
Relacement HepSleve to soil pipe adaptors are available, Hepworth code VA9.
For further advice, contact the Hepworth Drainage Technical Advisory Service on 0870 4435551
The Hepworth Plumbing Team
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http://www.hepworthdrainage.co.uk/pdf/technical_manual/application_application_details_2.pdf
Thanks for this. I see the plastic pipe doesn't go inside the clay pipe (although this would surely make the joint better and not rely on the 'rubber' seals). Of course the plastic pipe would need to be a smaller diameter.
My adaptor hasn't moved (permanently), I think the seal has just failed around the clay pipe. Maybe the plastic pipe was moved up and down slightly when I had a new toilet fitted a couple of years ago and the adaptor moved with it, breaking the 28 year old seal around the clay pipe.
I'll call the advice line.
Many thanks,
Darren.
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