The human vagina (meaning a "sheath" in Latin) is an elastic fibro-muscular organ in a female which bridges the external genital (or vulva) and the cervix of the uterus.
It has a relatively shorter and narrower size during a steady state unlike in its pleasurable state or when giving birth where it enlarges to serve the needed function.
The vagina also maintains a process of cleaning itself normally through secretions and discharges eliminating unwanted bacteria and microbes while keeping the wanted ones ("normal flora").
The normal flora consists of lactobacilli that produce lactic acid in the vagina responsible for warding off other invading microorganisms responsible for infection.
Lactobacilli strains (or another variation of lactobacilli) are found in yogurt.
Thus, yogurt-like vaginal smells or maybe less noticeable odor could indicate a normal vaginal smell.
When there is a deviation in which vaginal smells progress into something else, we might already suspect an abnormality with the vagina.
When the vagina smells pungent or rancid, it may indicate bleeding from an internal anatomical structure.
Fresh blood smells a lot less pungent than the ones which are already days old.
Foul fishy odor is another vaginal smell indicative of bacterial vaginosis.
The odor comes from the grayish-white discharge that the invading bacteria produce when causing vaginal infection.
In the event that Gardnerella or Mobiluncus morphotypes are present, overwhelming the amount of the normal lactobacillus inhabitants, they grow and multiply in the vaginal walls causing minor tissue damage contributing to the smell.
Chemically, the smell contains the odor given off by a hydrogen peroxide component.
Vaginal smells would stay normal if proper hygiene is followed.
Being careful not to introduce unwanted microorganisms is one way of preventing the acquisition of infection thereby doing away with the unwanted vaginal smell.
Some measures you could use are proper hand washing procedures, wiping with a clean dry tissue after urinating (don't use scented tissues since some products may either upset the pH-balance of the vagina while others promote bacterial growth), and not douching.
Douching is not recommended by doctors since as mentioned above.
The vagina has a natural way of internally cleaning itself.
Thus, there is really no need to introduce fluids inside the vagina except for diagnostic purposes.