Just have to study conjugation charts for verbs. In your question, пить is the infinitive (to drink), пьёт is for third person singular subject (he/she/it), пьют is for third person plural subject (they).
How do you make a difference between saying My horses are drinking AND My horses drink? Present tense vs continuous tense? Can someone clarify this one for me
Definitely пьют. Considering пьёт is singular and we are talking about more than one horse, you will want the 3rd person plural version, which is пьют.