Okay, if anybody can offer a solution:

Main gas pipe divides on aprox. 100 small diameter plastic pipes which drives natural has to each household separately.

All conections are aprox. same length except one, which is quite larger than other (100 m). Household's owner claims that he felt a strong sense of odorant (Tetrahydrothiophene) and somethimes petrolium, which is in fact true. There is one more important difference; he uses gas very very rarely, compared to others.

Please if anybody can give me an explanation why does this occurs, pipe is plastic with no damage (I suppose).

Thanks

Kresimir