Kaplan wrote:

I have a bathroom which is in the roof of my house where the waste pipe
leads into the attic. The house is 5 years old and last month I noticed
light leaking into the floor below (ground floor). It seems the sealant
has failed at a join. Is it reasonable to expect to reseal this pipe
without taking it out? There is no visible hole (there is only about an
inch or so space between the bottom of the pipe and the attic floor).

Could you clarify a bit... so is the bathroom in the attic? Does it's
waste pipe travel down through the ceiling to the ground floor? And the
pipe is dry above the attic floor and wet below it? Is that right?!

If so, you need to find the point where it's leaking; pull up the
floorboards or bathpanel or whatever to find the joint or hole. What
sort of pipework is it? Are there knurled rings around the joints which
you can unscrew (easy), or are the joints stuck or welded together?

David