( ( If necessary ) ( , ( ( ( use water ) ( from ( the ( bathtub ( to ( flush ( the toilet ) ) ) ) ) ) ) . ) ) )
(ROOT (S (PP (IN If) (ADJP (JJ necessary))) (, ,) (VP (VB use) (NP (NN water)) (PP (IN from) (NP (DT the) (NN bathtub) (S (VP (TO to) (VP (VB flush) (NP (DT the) (NN toilet)))))))) (. .)))
If necessary, use water from the bathtub to flush the toilet.
(ROOT (S (NP (NP (DT The) (NN action)) (PP (IN of) (S (VP (VBG flushing) (NP (DT the) (NN toilet))))) (, ,) (VP (VBN performed) (NP (JJ multiple) (NNS times)) (ADVP (RB daily))) (, ,)) (VP (VBZ is) (NP (NP (DT the) (ADJP (JJ single) (JJS biggest)) (NN use)) (PP (IN of) (NP (NP (NN water)) (PP (IN in) (NP (DT the) (NN home))))))) (. .)))