Here is the link from Raritan for the parts list and exploded view diagram of the PH II. If the joker valve becomes distorted in any way then it will allow fluid to feed back into the bowl. Before you rebuild the head, flush PLENTY of fresh water through so you don't get and back splash of the "good stuff". I have a WC , so I don't know if you can buy just the joker valve from Raritan. However, if you are fixing one part, you can bet that the other parts will go soon too. Once you get into a job like this you might as well replace all of the "consumable" or replaceable parts. Buy a full rebuild kit, or a whole new head unit. Sometimes the cost of the whole thing isn't all that more expensive than the rebuild kit. It's a matter of cost vs. convenience I guess. Check this link out either way (its a .pdf). Have fun, and remember to purge the thing with lots of water prior to taking it apart.