We should start tackling this problem like a rat up a drainpipe

A client told me last week, at the end of a consultation, that I was like a rat up a drainpipe. He was in such good humour, it clearly wasn’t meant as an insult but, having never before encountered it as a compliment, I was sufficiently taken aback to let him leave the building without getting him to elucidate what rats do up drainpipes and why I reminded him of one. Not asking him then and there was a mistake, because it’s not the kind of thing you can retrospectively ring a client to clarify.
The man in my life, who hails from rural Ireland, nodded appreciatively when I queried this with him. His eyes misting over as he looked into the middle distance of reminiscence, he said yes, that you’d often get a rat up a drainpipe and you’d have to hammer the drainpipe in order to make it disgorge the rat, after which you would hammer the rat. This confused me even more, for two reasons. 1) It related not at all to the client and me. 2) I couldn’t figure out why you would hammer a drainpipe to get a rat out of it. The great outdoors is full of rats. You don’t want them coming indoors. So if they decide to regard a drainpipe as modular housing, why not let them at it?