Since gaining ownership of s/v Kwaai I have had the pleasure of working on the head. I have had a constant problem of dirty water and clean water mixing and the dirty water being recycled through the bowl. Not to mention a constant stink. In Mazatlan I purchased a new 12v pump - well it cost a small fortune and did not fix the problem.On ebay I found a listing for "ELECTRIC MARINE LARGE DELUXE TOILET/HEAD 12V FOR BOAT" from seller baronusallcbarongroup - a complete unit for around $300 including shipping. Took it down to mexico on my last trip, installed it and it works perfectly.
On advise from a fellow mariner, I changed from raw water to drinking (chlorinated) water as a water source and there is no smell in the boat at all now.
As for the above ebay seller, I have purchased a lot products from this seller for s/v Kwaai and I am very pleased with pricing and quality.