Thanks DH for comment and advise regarding the rust.
However regarding this tube.
SohRon quotes:-
The two final parts that finish up the installation are the drain hoses for the filter/element case and the plenum. They come in two sizes, and while they may look similar, they're actually quite different
The longer hose is the plenum drain hose. It is has an internal foam filter
Foam filter. Remove this when using hose for drain on the filter/element case Its primary purpose is to drain any gas that might somehow escape the carbs and splash into the plenum. The foam acts as a kind of barrier that lets gas out but doesn't let in a lot of air or debris, so that the correct pressures are maintained inside the plenum during engine operation. It connects to the plenum via this outlet formed into the plenum body where it's secured by an omega clip
[/
This photo is of the Plennum (left) and Air Filter Housing (right).
... the plenum hose can still be had and, with a couple of mods, will work fine. Just cut it to length and remove the internal foam filter mentioned previously.....
I'm confused, do I leave the sponge in or remove it?! Does it drain or keep stuff out of the air filter housing
It finally dawns on me, the 500 doesn't have a Plennum drain, so there's no tube needed, therefore the sponge comes out as it's going into the filter housing; per SohRon's comment ... Foam filter. Remove this when using hose for drain on the filter/element case.
Problem solved unless anyone else disputes my finding.