Natal Neptune is the sign where your Neptune was placed during birth time, and from there other houses are calculated clock-wise.
If you were born with Neptune in Scorpio, then your natal house is Scorpio (Vrischika Rasi) and during transit, Rahu/Ketu forming conjunction (in Scorpio), sextile (aspect of 60° which are Capricorn and Virgo in this case), square (aspect of 90° which are Aquarius and Leo here), trine (aspect of 120° which are Pisces and Cancer here), opposition (aspect of 180° which is Taurus here) are discussed in this article.
Conjunction is transiting through same sign as in birth chart, sextile is transiting 3rd or 11th house, trine is transiting 5th or 9th house, opposition is transiting 7th house from natal sign.
Transit Rahu conjunct Natal Neptune or Transit Ketu Opposition Natal Neptune : This transit characterizes intuitive and prophetic insights. The native readily understands the cultural trends and beliefs. The native is psychologically well aware other’s attitudes and is able to adjust himself accordingly. Due to indecisive nature of Neptune he may not be able to get benefited from modern ways of doing things.
Transit Rahu Sextile Natal Neptune or Transit Ketu Trine Natal Neptune : Intellectual and intuitive awareness of the present trends is characteristic of this transit. The native is intuitively aware of the business or social activities around and plans to gain from these. The native hates enmity but has ability to make enemies work for him. The native may be intellectually interested in pursuits of art, music, entertainment, photography and psychology.
Transit Rahu or Ketu Square Natal Neptune : This transit characterizes confusions between idealism and hunger for power and material gains. The native either may follow destructive forces of the day, to bring his own disaster or withdraw from the activities going around. The native does not accept subconsciously the prevailing norms and beliefs. The native should not get trapped by bad habits at this time because there is every danger on the part of the native to follow social nuisances.
Transit Rahu Trine Natal Neptune or Transit Ketu Sextile Natal Neptune : This has similar significance of Transit Rahu Sextile Natal Neptune or Transit Ketu Trine Natal Neptune. However there is greater intellectual awareness of the traditional values. The native has intuitive inspirations to understand spirituality, psychology, and philosophy. The native can easily distinguish between traditional values and present cultural trends and has the ability to defend both of these on their merits and demerits.
Transit Rahu Opposition Natal Neptune or Transit Ketu conjunct Natal Neptune : Spiritualism and withdrawal from social involvements characterize this transit. The native is not able to attune himself subconsciously neither with the present trends of the society nor with the traditional beliefs. The native tends to withdraw from social involvements and remains in seclusion. The native acquires misunderstanding with daily acquaintances. This transit is conducive for spiritual advancement than material progress.