I'm warming to the idea of using flannels in the shower - the running water rinses out any nasties, so you are basically using a clean flannel each time on different aeas of the body.
But, filling a sink with lukewarm water and using that small amount of water to 'strip wash' the entire body still makes me heave.
Lets take this from the top:
You fill a basin with water and take a flannel.
a) Flannel is swiped across the face and picks up a load of makeup (if a man - you wipe across head quickly and the flannel also picks up hair grease and dandruff)
b) Flannel is then rinsed in basin and squeezed out.
c) Flannel containing traces of makeup and hair grease is then used to wash armpits, where it picks up a load of sweat.
d) Flannel is rinsed in basin.
e)Flannel containing makeup, hair grease and sweat is then used to wash your bits (which probably weren't even that dirty, but will be now).
f) Flannel is rinsed in basin.
g) Flannel containing makeup, hair grease, sweat and fanjo debri is then used to wipe round the back end. 
I then presume you move down to the feet? At which stage it would probably be more hygienic to wee on them to get them clean than use the soup that is in the basin!
It's basically transferring dirt around onto different parts of the body. The only place that gets a good clean is the face.
I think this is why most Americans are disgusted at baths as a means of getting clean - really speaking, you are lying in your own filth.
A bath's OK for relaxing.