wrote:
I thought the russian service module was equipped with all kinds of
hygienic stuff...

It does have a toilet. But no clothes washing machine, and no shower.

They wash themselves by hand only then? For several months?

Yes.

What does the space station smell like from inside?

Fortunately, in space the sense of smell is somewhat dulled by body
fluids redistributing themselves evenly throughout the body (instead of
being pooled by gravity), which clogs the sinuses a bit. It affects
taste for the same reason; astronauts tend to prefer spicier foods in
space than they would eat on the ground. The number one food item among
NASA astronauts is shrimp cocktail loaded with horseradish.

Nevertheless, some smell does come through. The interior smell of ISS
has been compared to a locker room, though different crewmembers report
different impressions.