fueling hardware

[aion at sdf.lonestar.org (E.Noval)]

I finally put my new gastank in today -- found out that it was rotted out 
around the the two lines (return/vent) on the top/passenger side of the 
tank. Nice big hole.

Im wondering what the purpose of the small white plastic rectangular box 
is for (near the fuel pump) -- besides mating two different hoses 
together.

Is it necessary? Does anyone have the Etka number for it?
Id like to check how much they are at VW cause mine is partially cracked.

Thanks
Ed
87 mk2