If you're happy too it might be worth replacing the external drains. Recently did mine and although it's hard work I hopefully won't have to worry about it for a long time, if at all. Plus I've added a few more gulley's so should shit get clogged (ha!) I can easily rod them.
I'd want to get them replaced if they are old and crusty. We will get the front garden completely done up in the not too distant so I want to get this done first.
Inside or outside?
I've got to look at our external drains. I am not relishing the prospect. I do have a PW and the unblocking attachment though....
It will probably just crack our ancient Edwardian pipes though won't it? sigh