This particular toilet is sold on the premise that a large 4" tank opening will create a stronger flush using a small amount of water. It's a great idea if the tank is large enough to allow the arm on the handle to lift the flapper high enough to have a complete flush. This one, in my opinion, is not. I have contacted Jacuzzi asking what I can do to correct this problem. They have yet to "get back to me" after 2 weeks. I don't think they have an answer. I don't think I'll be purchasing any more Jacuzzi products, unless they can give me a practical solution.