The Brew Cabin

I need to connect to a damaged 100mm (internal size) plastic drain pipe which in embedded in hardened concrete under my garage. What makes it worst is the the end of the pipe in under a non supporting pillar and I don't wish to upset the foundations any more than I have already. Every time I chip at the surrounding hardened concrete around the pipe it is so hard the splinters damage the pipe.

I know it is not ideal but I am thinking of inserting another tube (with an external 100mm measurement and 3 mmm think) and gluing it in place and then glue another peice of the existing pipe with (internal size 100mm) to make the join.

I know a small amount of water will never naturally drain away, but at the decline is steep this should be minimal.

Sorry if I have gone on a bit, but any help would be very much appreciated.

The correct way to do this is to use a small angle grinder or similar to cut away the concrete surround, a bit at a time, until there's sufficient room to accommodate a coupling.

Your plan is feasible, but somethijg I would only use if there was no other option and on a SW system. I'd be reluctant to use it on a FW system just in case the lip formed by the internal coupling piece was to snag something, and "Feminine Hygiene Products" are a particular nuisance in this regard.

If you could fashion the proposed internal coupling to eliminate the lip by chamfering the upstream edge, that would be advantageous, but I repeat that use of a proper external coupling is preferable.