Hi, I wonder someone could advise about the drain system from a residential house: For a building of less than 25 years it says it will probably have separated surface water drainage system, (other than the foul drain). Directing rain water into the foul drain is not allowed due to the building regulation. The house I am buying has this issue exactly and the survey report suggests that remedial work may be required and may be expensive. Should that be a concern to me as it says [may be expensive]. What's your opinion Fussy or necessary? Thanks!