fish tank newbie - what is a tube with bung?

[Biggsie]

I have inherited/rescued a fish tank complete with fish and accessories from an abandoned home. Everything seems to be OK but there is an unexplained bit of kit.
It is a quantity of clear tubing with a hard bung at one end. Is it somesort of syphon? Any ideas please?

[B00]

A syphon, for sucking the water out.

[Prudie]

and poop off the bottom (of the tank!)

[snags]

Also used for sucking up/out uneaten food and fish sh!t.

[woofgang]

Is it an airstone?
http://www.aqua-fish....hp?h=aquariumairstone
Scroll down the page to two small pictures

[Duncer]

Alternatively, buy some ugly little bottom dwellers, more commonly known as Jedward fans, and they will eat the dirt/poop/debris.