GERUND AFTER PREPOSITIONS

I feel slightly embarrassed to have to repeat this subject, but you people keep making the same mistake:

After prepositions you must use the gerund in English:

He left after drinking his beer / se fue después de beberse la cerveza.

Clean the kitchen before leaving / limpia la cocina antes de marcharte.

Thank you for accepting my offer / gracias por aceptar mi oferta.

On entering, he fell / al entrar, se cayó.