Is he neutered? If not, do so now. It may be the beginnings of marking
behavior.

Is the other cat a male? Again, this may be marking behavior. It may
also be the other male preventing him from using "his" box now that the
kitten is maturing into an adult. Sometimes they do that.

In that same vein: Do you have a separate box for each of them? Some
cats hate to share. Your kitten might, or your adult might.

Have you changed litter recently? If so, he may not like it.

Has the pan been totally cleaned, litter replaced and box disinfected,
within the last 2 weeks? If not, do so. If so, did you use a harsh
cleaner that he may not like the smell of? Many cats hate bleach.

Have you cleaned your bathroom with ammonia or a product containing
ammonia? This can make a cat want to pee there.

Has he been to the vet lately? He may have a minor bladder infection or
other physical cause.

For preventative measures, fill the tub an inch or two with water. He
won't go there again. However, this may cause him to urinate elsewhere
if the real problem is one of the above (or another physical or
behavioral problem). I'd rather have the cat pee in the tub than on my
carpet. You may want to just let him go there until you check out his
health and other possible situational causes.
You may also consider putting a small litter pan in the tub in the
meantime while you are checking out causes. They have disposable ones
with litter already inside at many stores for like $3, including Walmart
and Petsmart.

-------------------------------------------------
~kaeli~
Jesus saves, Allah protects, and Cthulhu
thinks you'd make a nice sandwich.
http://www.ipwebdesign.net/wildAtHeart
http://www.ipwebdesign.net/kaelisSpace
-------------------------------------------------

Take the kitten to the vet. He may have a urinary tract infection.
Gail

We used to have a cat who did the same thing.  He started using the tub
as a litter box when he was a kitten.  I think the problem originated
because my husband-to-be had put the litter box in too close proximity to

the food dishes, and the cat preferred a nice, quiet, dark place for his
toilet activities!

Try putting another litter box in a private location (you should have
more than one anyway, when you have more than one cat), and show it to
this kitten, and praise him if he uses it.  At the same time, keep the
bathroom door closed.  If you nip it when he's young, you may be
successful.  We didn't have a lot of luck with our Oreo, because we
didn't keep the bathroom door shut (rather stupid of us I'd say, in
retrospect!), and he kept up the habit until we bought a new tub - and he

just didn't like it for some reason!

By the way, if he uses other areas as toilet areas, definitely get him to

the vet, because that is a sure sign of physical problems.

HTH,
Deb