An assembly comprising: A) a drain for sanitary fixtures, provided with: A1) a plug axially movable between a lowered position, in which the plug does not intercept the upper opening of the housing of the aerator referred to in point B, thus allowing the passage of water, and a raised position, in which the plug intercepts said opening and prevents the passage of water, and A2) an overflow mechanism, which supports the plug and which is calibrated so that to yield at the exceeding of a predetermined value of hydrostatic pressure acting on the plug itself, thus causing the lowering of the plug, and, therefore, the draining of the water through the drain, characterized by B) an aerator comprising a body delimiting a housing that can be crossed by a flow of water, in which the drain is inserted, and B1) a channel fluidically connecting a lower portion of said housing with the outside, B2) a floating element housed in the channel, movable between an active position, at which it sealingly intercepts the channel and prevents the rising and spillage of water through the channel itself, and an inactive position, at which it does not intercept the channel or it only partly intercepts it, and the channel can be crossed by a flow of aeration air entering said housing and drawn back towards the drain. A) a drain for sanitary fixtures, provided with: A1) a plug axially movable between a lowered position, in which the plug does not intercept the upper opening of the housing of the aerator referred to in point B, thus allowing the passage of water, and a raised position, in which the plug intercepts said opening and prevents the passage of water, and A2) an overflow mechanism, which supports the plug and which is calibrated so that to yield at the exceeding of a predetermined value of hydrostatic pressure acting on the plug itself, thus causing the lowering of the plug, and, therefore, the draining of the water through the drain, characterized by A1) a plug axially movable between a lowered position, in which the plug does not intercept the upper opening of the housing of the aerator referred to in point B, thus allowing the passage of water, and a raised position, in which the plug intercepts said opening and prevents the passage of water, and A2) an overflow mechanism, which supports the plug and which is calibrated so that to yield at the exceeding of a predetermined value of hydrostatic pressure acting on the plug itself, thus causing the lowering of the plug, and, therefore, the draining of the water through the drain, characterized by B) an aerator comprising a body delimiting a housing that can be crossed by a flow of water, in which the drain is inserted, and B1) a channel fluidically connecting a lower portion of said housing with the outside, B2) a floating element housed in the channel, movable between an active position, at which it sealingly intercepts the channel and prevents the rising and spillage of water through the channel itself, and an inactive position, at which it does not intercept the channel or it only partly intercepts it, and the channel can be crossed by a flow of aeration air entering said housing and drawn back towards the drain. B1) a channel fluidically connecting a lower portion of said housing with the outside, B2) a floating element housed in the channel, movable between an active position, at which it sealingly intercepts the channel and prevents the rising and spillage of water through the channel itself, and an inactive position, at which it does not intercept the channel or it only partly intercepts it, and the channel can be crossed by a flow of aeration air entering said housing and drawn back towards the drain.