I would also suggest getting rid of the sand sifting star, and if you don't have it yet, stay away from it. It is a known fact that they starve to death in our aquariums because there is not enough food for them to survive, in our sandbeds. They will die, and most likely will die buried in the sand, which could pose a threat to your tanks ecosystem and all of its inhabitants. Besides, sea stars should not be placed in fairly new tanks. They need well-matured tanks with as little water fluctuations as possible.
If you look on the websites provided by this site, to all the vendors of fish and fish supplies, they usually have the tubing your looking for.
What i did was have a couple small containers, like Tupperware, then fill it up with water from the bag the animals are coming from. Get the tubing, and tie a knot in it near the middle connecting from your tank to the container you have your fish/inverts in. With this loose knot, you can control the water flow and can adjust it easily by pulling on both sides of the tube to tighten it, or pushing the two ends of the tube closer to eachother, which will loosen the knot and allow more water to flow through. As the water begins to fill up in the container, you just take a cup or another small container and then scoop out the water little by little. You shouldn't be replacing half the water on one scoop though, it should be a gradual decrease. That's what acclimating is all about.
To get a better understanding of the concept if you can't understand what i said(it's been known to happen :p) then you should read this excellent article: