Jisho

Ask yourself: does this verb take a direct object?

If the answer is yes, it's a transitive verb.

As simple as that.

Fredora is generally very much correct.

However, one should also know that transitivity is not always black and white. Firstly, don't forget that を also has other usages besides marking the direct object (like "through"). But even with that out of the way some verbs aren't just a 100% transitive or intransitive. Take a look at some of the examples here: https://bibdb.ninjal.ac.jp/bunken/ja/article/100000135697 ("本文表示" at the bottom) There are also verbs that seem at first glance like they're standard transitive-intransitive pairs (like 間違う-間違える, 終わる-終える-終わらせる, 触る-触れる) but where real-life usage is much more involved and cannot be reduced to just their presumed transitivity.

That said, 飲まれる is intransitive. Btw, it's not really Jisho.org who says so, it's JMdict. Just go there and change the corresponding entry.