Because they have no fur, the Sphynx cat will pick up dirt just like your own skin. So just like
you they need to be bathed. How often depends on the amount of oil in their skin- they are
all different. Some will not need a bath for several weeks while others need one weekly.
More than weekly is not recommended as their skin will produce more oil to compensate for
frequent baths. I only have one cat that requires more bathing and I use a throw away kitty
wipe
to keep his chest and stomach clean between baths. They are called "Perfect Coat Bath
Wipes" , which I find in the pet section at the grocery store. There are several products out
there that are similar and work just as well.
Begin by filling the sink with no more than two inches of water or
just past their "ankles" . I've found they don't mind the water so
much if there isn't a lot of it. (The first time I bathed my first Sphynx
I filled the sink up past his tummy which he didn't appreciate. I know
this because I chased wet kitty prints all over the house until I
found him behind the washer.)

With your hands gently wet him down (running water from the
faucet will terrify him.) and/or squeeze water from a washcloth.

FIll your hands with a good natural shampoo for cats or Epi-Soothe
from your vet (believe it or not baby shampoo is too harsh.) Work
the shampoo in over the body, avoiding the face. I use a baby
washcloth to scrub the stubborn places like the chest.

Do not use shampoo on their face. Rinse the washcloth and then
wipe their face, eyes, and ears clean- they actually seem to enjoy
this part.

Wrap your kitty in a towel and dry them. By now they will probably
be squirming to get down! Let them go and watch how quickly they
recover from their "ordeal". Within a couple of seconds (literally)
they will be running around like he was never immersed in a
disgusting tub of water and scrubbed as if they couldn't clean
themself! (Hmmph)