strainer

noun

1. A device through which a liquid is passed for purification, filtering or separation from solid matter; anything (including a screen or a cloth) used to strain a liquid.
2. A perforated screen or openwork (usually at the end of a suction pipe of a pump), used to prevent solid bodies from mixing in a liquid stream or flowline.
3. Debris in water that blocks the passage of solid objects.

   “A strainer is something on the surface of the water that allows water to pass through it but not solid objects, like boats and people. Strainers are likely to consist of fallen trees, old fencing, guardrails […]”

4. One who strains.

   “An important factor with respect to recurrence [of rectal prolapse] is the fact that many of these patients are chronic strainers.”