Well guys. Back when they were making these... They put water in at the top. How? Tiny little hole before completely sealing it there. They used a very tiny needle. (Like what you see that look like a medical shot, but smaller) When they filled it with water, they then covered the hole they made with clear plastic. Then basically heat up the top keeping the hole covered. Once the plastic is shaped and melted it is sealed completley.
So because of that reason... They don't com apart anywhere. However if you did make a hole at the top with like a Small dremmel or drill... That'd be the only way to get into the tube to clean it. Seriously, have a parent or person who knows what they are doing do it FOR YOU. Then once you have the hole made, go inside with a q-tip once the water is dumped out. Then once it looks clean, add a dab of water on the q-tip or inside the tube. (Not fully) Then scrub with the Q-tip. Then repeat with a bit of bleach. (Windex glass cleaner should work as well) Then once it looks clear and clean.... Finally add water. Make the water be about full like 4/5ths.
Then to seal it, you need some serious glue. Like Super glue or Gorilla Glue. Then once dry, make sure to apply another layer or two. Let DRY. (Give atleast 10-15 minutes between layers) To make sure it is sealed, use this simple task. Make a small container of soapy water. On the top where you made the hole... If there is a hole still, it will bubble where the hole is. So if there is a hole, cover it with super glue in the spot. Then repeat placing water over where the hole was. Keep testing for holes.
It maybe wise if you try/do this, to check for holes every once in a while.
I have not done this myself and cannot be held responcable if something happens to your Aquapet. Many people have been wanting to clean their pet out... This is of risk of your own.