Closing waste entry point

I have found while digging along the side of the house, and old sewer connection from what would have been the bathroom. It was a terracotta 3 way level with vent. It has been covered over with a board, and I need to go a bit lower. I can see that it T's into the pipe that runs horizontally about 6-700mm lower down. Which still has waste running through it.

So the question is. How do I block this pipe off lower down, and do it in a better sealing way than just a board?

Is there a plug that can go all the way down with a half round concave shape to form a new roof of the pipe where it branches up?

One suggestion I was given was to put balled up newspaper, and then cement on top of that, and if the paper breaks up and falls down, no probs.

Another suggestion was a plastic bottle?

Earthenware branches are sealed with sand and cement as you suggested.

Tools

Remove the bit of earthenware pipe down to the next collar if possible, clean the collar out without breaking it if possible, cut yourself a bit of villa board or lead sheet to fit inside the collar and use sand and cement to seal it.

Being earthenware pipe, I would only cap/plug it off if you have easy access to your sewer close by. If you havn't, you would be much better of bringing it to surface and having a point a point of access for when the drain blocks. If its not blocking at the moment, it is only a matter of time with the old pipes(could be 10 years or 10 weeks). So when the plumber comes round to unblock, he will have an easy point of access and hopefully get the job done quicker without digging around looking for an I.O. I spent 3 hours on Monday looking for the point in a yard that the last plumber went down but was too lazy to bring to surface. The last plumber could have saved the customer my extra labour by using a bit of common sense.

I dug down to the collar on the upsidedown T junction. Put a tin lid in the hole which was smaller than the collar, but bigger than the internal of the pipe entry. Then poured some mixed concrete into the collar. Worked well.