The affixes ktvā , kta and ktvātu optionally get the iṭ augment after pū,
As पूत्वा or पवित्वा, सोमोतिपूतः, सोमोतिपवितः पूतवान् or पवितवान् ॥ This allows option where by 7.2.11 there would have been prohibition. See 1.2.22.,
पूङश् च
Adhyāya 7 · Pāda 2 · Rule 51