To tell if you add en or et or n at the end of a word to create the definite form, you have to look at the ending, and the gender prefix. Add an en at the end of the word if it is an en word, that does not end with a vowel. Add an n at the end of the word if it is an en word, that ends with a vowel. Add an et at the end if it is an ett word. There are few weird ones still like vattnen.
You can see the spelling here. The word dricker doesn't sound very good in the automated version. On this page there are currently 3 recordings of native speakers saying it: http://sv.forvo.com/word/dricker/#sv
Imho the second speaker, lither sounds best. (camelkebab got a little too close to his mic but the third one is good too).