What is Mud Box in sea water pipe line and the purpose of it?

What is Mud Box in sea water pipe line and the purpose of it?

Mud boxes are fitted into the machinery space bilge suction piping. The mud box is a coarse

 strainer with a straight tailpipe down to the bilge. To enable the internal perforated plate to be cleaned when necessary, the lid of the mud box is easily removed without disconnecting any pipe work.

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