Keep in mind, first, that the Tendou-ke is a two-story residence, 
with an add-on building (the dojo), and six bedrooms (one per 
daughter, Soun's room, the guest room Ranma and Genma sleep in, the 
room Happousai sleeps in). Now, it stands to reason that in any house 
this large, you would have one furo and two toilets.

So, here is how I believe the bathroom layout of the Tendou-ke is:

-One furo, located on first floor
-Two toilets: one located near first floor furo, other located on 
second floor.

Anyone is welcome to dispute this, but for the sake of everyone's 
sanity, is it not safer to assume?

In the anime (at least), there is only one toilet. It's in the room
past the door on the left, when you enter the change room/laundry.
Upstairs, there aren't any toilets. (I was looking at the 'blue
prints' of the Tendou-ke.)

                                                  == or =   Doorways
    _________________                                   =
    I  ___________  I_______________________
    I I           I__===__________===_______I
    I I Living    I          I I       =I   I  <= Entry to toilet
    I I Room      I Happi's  I I Change I_=_I
    I I           I Room     I I Room   I   I  <=  Toilet
    I I_______==__I          I_I__===___I___I
    I I_IBC?_I    I__________I I        I
    I             I IBC?     I I Bath   I            IBC = In-built
____I__________   I__________I I Room   I                  Cupboard
I I            I  I          I I________I          ___________________
I I            I =I Kitchen  I                     I
I I Souun's    I =I          I                     I
I I Room       I  I__________I_ _ _ _ _ _ _ _ _ _ _I
I I            I             I  Walk Way to Dojo  =I     Dojo
I I____________I      _______I_ _ _ _ _ _ _ _ _ _ =I
I  _______      ______I      I                     I
I_I__===__I_____ILLLLLI______I <= Landing          I__________________
  I_______I
                   ^- Stairs
     ^- Front Door

GROUND FLOOR
----------------------------------------------------------------------
1ST FLOOR

   _____________________________________
   I           I           I           I
   I Kasumi's  I Nabiki's  I Akane's   I
   I Room      I Room      I Room      I
   I           I           I           I
   I________==_I__==_______I__==_______I
   I   I=                              I
   I___I=________    __________________I
   I I.B.C?     I    I
___I____________I    I
I               I    I
I Guest Room    I    I
I               I    I
I               I    I
I               I    I
I_______________I    I
I      I=            I
I______I=________    I
       ILLLLLLLLI    I
       ILLLLLLLLI____I

        ^- Stairs

Well, it's not quite to scale, but that's the best that I can do in
ASCII ... But there's no-where on the second floor where a toilet
can be. Only on the first.

Plus, I think that a toilet upstairs is a bit extravagent, especially
since the house is rather old (or else the Tendou family wouldn't be
able to have it where it is!) ... the 2nd floor was probably built on
when Mr and Mrs Tendou had the three daughters (remember - these rooms
are all modern rooms, so they wouldn't have been built there right from
the start!). So why would you need two toilets for a family of 5? O_o
It may be nice to have it, but if you're not rich enough to afford the
plumbing ....... (One can assume that they used all their spare cash
on building a second floor! Why pay extra for plumbing when there's
just three girls and you and your wife?)

You must remember that the original house had only TWO bedrooms. All
the others were added on later!

Kun-chan...
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