50 mm Uniseal (Black)
A Uniseal is used to create a water tight seal around the circunference of a pipe going through a hole on a tank or aquarium.
Uniseal is also available in the following diameter:
the sturdy rubber makes it a very snug fit, and being one piece makes it much quicker and easier to attache, making the plumbing of getting fluid around from any shape vessel to another a breeze
Awesome product when you've tried all the other avenues and failed. just a tad expensive.