To dirl does mean to vibrate, but it also means to thrill; hence, a dirler is a thriller, something that excited the user of the word. An English equivalent might be the rather old-fashioned 'hummer'...and I don't mean a Schwarzenegger 'tank'! Even 'humdinger' is rarely heard nowadays, but that's the basic idea here.
Chamber-pot! I was born and brought up in a Doric-speaking environment and the only word for chamber-pot we ever used was chuntie or chanty. I suspect, therefore, that dirler was used by the rustic community rather than the townsfolk of north-east Scotland.
(The worrying thing is that I had totally forgotten I had a Doric dictionmary right there on my bookshelves!)
The chamber-pot meaning obviously harks back to Barmy's earlier response, in that it refers to the vibrating sound created when the device was used!
There's a bothy ballad somewhere that describes a couple of rakes trying to look into a girl's bedroom and getting a 'dirler' thrown at them for their pains - can't remember if it made it clear whether it was empty or not!