The version sung to Cwm Rhondda at St Andrews University in my day (1959) was (repetitions omitted)

You must eat when you are hungry.
You must drink when you are dry.
You must rest when you are weary.
Don't stop breathing, or you'll die.

Father's pants will soon fit Willie.
Will 'e wear 'em? Willie will.
Will 'e wear 'em, will 'e wear 'em,
Will 'e wear 'em? Willie will.

The tradition of setting undignified words to hymn tunes seems to me to be even stronger in Britain than in America.