What are they talking about with Ben in Rise Of The Nutters?

I'm not British, so I'm not exactly sure what's being said here:

Malcolm:

Right, Ben, heard the big news about Paxo. Oh, right. What was it you did in your gap year again?

Ben:

Um, InterRailing, month on a kibbutz.

Malcolm:

Did you ever travel, like, 100 miles per hour head-first through a tunnel full of pig shit? Because that's what's going to happen to you tonight with Paxman, unless Unless you listen to us.

Jamie:

He will eat you up, sick you out and grout his fucking wet room with you.

Ben:

Yeah, I have been interviewed on television before, thank you very much.

From this link

Why is Ben's "gap year" relevant? Is this "tunnel of pig shit" expression just there for added vulgarity or does it have some British back story that I'm not aware of? And what is the nature of this grouting expression?

dialogue the-thick-of-it

Best Answer

Jeremy Paxman has a reputation for being an aggressive interviewer (based in particular on a famous interview with Michael Howard).

Interrailing around Europe has a reputation a fairly common activity in the gap year between school and university, especially in the 80s.

Malcolm was asking about a presumably leisurely time in Ben's life, to contrast it with the harrowing, stressful time he was about to be put through.

The tunnel of pigshit is just a colourful turn of phrase to describe the experience of being interviewed as an MP by Paxman.

The grouting expression isn't a particular idiom or known joke; grout is a paste for applying ceramic tiles to a wall, so it's just another creative turn of phrase to imply that Paxman will interview aggressively enough to liquify him. How jolly.