Here in the US you can buy beer in large glass bottles called "growlers". The term goes back to the 19th century when it was common for working men to bring home a pail of beer at the end of the day. These containers apparently had a tight fitting lid and the sound of carbon dioxide escaping as they were carried reminded someone of a growling noise.
The phrase "rushing the growler" meant sitting down for a couple of beers.
In that context this sign at the local wine and spirits shop makes perfect sense.
However in the UK I would not advise walking into a place and saying that you wanted your growler filled. And I fear that mentioning Wet Hops would not help clarify matters.
Really, you should just trust me on this one.