You do not usually need to apply for planning permission for repairs or maintenance on drainpipes, drains and sewers.
Although the work itself may not require planning permission you should clarify ownership and responsibility before modifying or carrying out maintenance. Drains, sewers and manholes may be shared with neighbours or owned by the relevant sewerage undertaker.
Failure to confirm these details or to comply with relevant standards/legislation could lead to legal and remedial action at your own cost.
If you live in a listed building, you will need listed building consent for any significant works whether internal or external.