A separation assembly for enabling separation of a fluid sample into first and second phases, comprising: a collection container having a first end, a second end, and a sidewall extending therebetween; a closure adapted for sealing engagement with the first end of the collection container; and a separator (40, 40C, 40D, 140, 140A, 240, 240A, 340, 440, 540) having a through-hole (46, 46C, 46D, 146, 146A, 246, 246A, 346, 446, 546) defined therethrough for allowing fluid to pass therethrough, the separator (40, 40C, 40D, 140, 140A, 240, 240A, 340, 440, 540) comprising: a float (42, 42C, 42D, 142, 142A, 242, 242A, 342, 442, 542), having a first density; and a ballast (44, 44C, 44D, 144, 144A, 244, 244A, 344, 444, 544), having a second density greater than the first density, wherein a portion of the float (42, 42C, 42D, 142, 142A, 242, 242A, 342, 442, 542) is connected to a portion of the ballast (44, 44C, 44D, 144, 144A, 244, 244A, 344, 444, 544); a first sealing perimeter; and a second sealing perimeter, characterised in that the separator (40, 40C, 40D, 140, 140A, 240, 240A, 340, 440, 540) is adapted to deform and transition upon applied rotational force from a first position in which the first sealing perimeter provides a sealing engagement with a first portion of the collection container while allowing a sample to pass through the through-hole (46, 46C, 46D, 146, 146A, 246, 246A, 346, 446, 546) into the collection container to a second position in which the second sealing perimeter provides a sealing engagement with a second portion of the collection container while maintaining a barrier for separation between the first and second phases, wherein the through-hole (46, 46C, 46D, 146, 146A, 246, 246A, 346, 446, 546) is defined along a through-axis and the first sealing perimeter is at a first orientation with respect to the through-axis and the second sealing perimeter is at a second orientation with respect to the through-axis. a collection container having a first end, a second end, and a sidewall extending therebetween; a closure adapted for sealing engagement with the first end of the collection container; and a separator (40, 40C, 40D, 140, 140A, 240, 240A, 340, 440, 540) having a through-hole (46, 46C, 46D, 146, 146A, 246, 246A, 346, 446, 546) defined therethrough for allowing fluid to pass therethrough, the separator (40, 40C, 40D, 140, 140A, 240, 240A, 340, 440, 540) comprising: a float (42, 42C, 42D, 142, 142A, 242, 242A, 342, 442, 542), having a first density; and a ballast (44, 44C, 44D, 144, 144A, 244, 244A, 344, 444, 544), having a second density greater than the first density, wherein a portion of the float (42, 42C, 42D, 142, 142A, 242, 242A, 342, 442, 542) is connected to a portion of the ballast (44, 44C, 44D, 144, 144A, 244, 244A, 344, 444, 544); a float (42, 42C, 42D, 142, 142A, 242, 242A, 342, 442, 542), having a first density; and a ballast (44, 44C, 44D, 144, 144A, 244, 244A, 344, 444, 544), having a second density greater than the first density, wherein a portion of the float (42, 42C, 42D, 142, 142A, 242, 242A, 342, 442, 542) is connected to a portion of the ballast (44, 44C, 44D, 144, 144A, 244, 244A, 344, 444, 544); a first sealing perimeter; and a second sealing perimeter, characterised in that the separator (40, 40C, 40D, 140, 140A, 240, 240A, 340, 440, 540) is adapted to deform and transition upon applied rotational force from a first position in which the first sealing perimeter provides a sealing engagement with a first portion of the collection container while allowing a sample to pass through the through-hole (46, 46C, 46D, 146, 146A, 246, 246A, 346, 446, 546) into the collection container to a second position in which the second sealing perimeter provides a sealing engagement with a second portion of the collection container while maintaining a barrier for separation between the first and second phases, wherein the through-hole (46, 46C, 46D, 146, 146A, 246, 246A, 346, 446, 546) is defined along a through-axis and the first sealing perimeter is at a first orientation with respect to the through-axis and the second sealing perimeter is at a second orientation with respect to the through-axis.