Amoebae survive in hypotonic environments because they have contractile vacuoles to pump excess water out of the cell. I couldn`t find a good video about amoebae, but here is a good video showing CV surgery in paramecium. The contractile vacuole, as the name suggests, expels water from the cell by contracting. The growth (water retention) and contraction (water excretion) of contractile vacuoles are periodic. A cycle lasts several seconds, depending on the type and osmolarity of the environment. The stage at which water flows into the CV is called diastole. The contraction of the contractile vacuole and the expulsion of water from the cell are called systole. A contractile vacuole (CV) is a subcellular structure (organelle) involved in osmoregulation. It occurs mainly in amoebae and in unicellular algae. Previously, it was called pulsating or pulsed vacuole.
Paramecium and Amoeba have large contractile vacuoles (average diameters of 13 and 45 μm, respectively), which are relatively comfortable to isolate, handle and study. Chlamydomonas, with a diameter of 1.5 μm, includes the smallest known contractile vacuoles. In Paramecium, which has one of the most complex contractile vacuoles, the vacuole is surrounded by several channels that absorb water from the cytoplasm by osmosis. Once the channels have filled with water, the water is pumped into the vacuole. When the vacuole is full, it expels water through a pore of the cytoplasm that can be opened and closed.  Other protists, such as Amoeba, have CVs that move to the surface of the cell when they are full and undergo exocytosis. In amoebae, contractile vacuoles collect excretory waste such as ammonia from the intracellular fluid by diffusion and active transport. The number of contractile vacuoles per cell varies by species.
Amoebae have one, Dictyostelium discoideum, Paramecium aurelia and Chlamydomonas reinhardtii have two, and giant amoebae, like Chaos carolinensis, have many. The number of contractile vacuoles in each species is generally constant and is therefore used for the characterization of species in systematics. The contractile vacuole has several structures in most cells, such as membrane folds, tubules, water channels, and small vesicles. These structures were called spongiomas; The contractile vacuole, along with the spongioma, is sometimes called the « contractile vacuole complex » (CVC). The spongioma performs several functions by transporting water into the contractile vacuole and locating and docking the contractile vacuoles in the cell. Water always flows first from outside the cell into the cytoplasm and is then moved from the cytoplasm only into the contractile vacuole for expulsion. Species that possess a contractile vacuole usually always use the organelle, even in very hypertonic environments (high concentration of solutes), because the cell tends to adjust its cytoplasm to become even more hyperosmotic than the environment. The amount of water expelled from the cell and the rate of contraction are related to the osmolarity of the environment.
In hyperosmotic environments, less water is expelled and the contraction cycle is longer. Contractile vacuoles absorb excess water and waste from the cell of a microorganism and excrete them into the environment by contraction. Water is transmitted by osmosis through the cell membrane of the amoeba. The contractile vacuole is a special type of vacuole that regulates the amount of water in a cell. In freshwater environments, the concentration of solutes is hypotonic, lower outside the cell than in the cell. Under these conditions, osmosis causes the accumulation of water from the external environment in the cell. The contractile vacuole acts as part of a protective mechanism that prevents the cell from absorbing too much water and possibly lysing (tearing) due to excessive internal pressure. The CV phases for water collection (expansion) and water expulsion (contraction) are periodic. A cycle lasts several seconds, depending on the type and osmolarity of the environment. The stage at which water flows into the CV is called diastole.
The contraction of the CV and the expulsion of water from the cell are called systole. Water always flows into the cytoplasm from outside the cell; Species that have a CV still use it, even in very hypertonic environments (high concentration of solutes), because the cell tends to adapt its cytoplasm to become even more hyperosmotic (hypertonic) than the environment. The amount of water expelled from the cell and the rate of contraction are related to the osmolarity of the environment. In hyperosmotic environments, less water is expelled and the contraction cycle is longer. .