Sorry i'm a complete novice and could really use some advice

I have been reading up on the T25 Aircooled heating for the past few weeks as mine doesn't work at all and went to take a look tonight and found that it's practically shot. Rust has eaten away at everything and it's all come apart. Pics below of nearside and offside, the tubes further along have also fallen apart from wear.


Whilst i was under the van i noticed quite a large wet patch under the engine which seems to be coming from the following device, smelt like fuel. I pulled on some of the hoses to see if any were loose at the black hose in the picture below practically fell off. My question is.. what is the device and where does the other end of the black hose go and what does it do? We have planned to use the van in a couple of weeks time but this is worrying me!

Any help is appreciated!

Thanks