The verbs in this post end in a vowel in the stem of the verb. When the stem ends in a vowel, the suffix या is attached to the stem of the verb.

This is the stem of the verb to drink: पी

I drank water – मैंने पानी पीया

We drank water – हमने पानी पीया

You drank water – आपने पानी पीया

He drank water – उसने पानी पीया

She drank water – उसने पानी पीया

They drank water – उन्होंने पानी पीया

Couple of clarifications:

1) water = पानी, पी = verb stem (to drink), या = suffix

If the past indefinite perfect tense is still shaky, check back at the previous post. It may clarify some issues.