If I do replace one or both toilets they will last for years and years ... I hope. 3. Create tables that show how much I will spend over the long run with each type of toilet. Consider the upfront purchase, installation and monthly water costs for each toilet type. Old Toilet -5 GPF 1.28 GPF 1.0 GPF Years Cost Years Cost Years Cost $ $ $ 1 1 $ 2 2 N $ 3 3 $ n n If I do replace one or both toilets they will last for years and years ... I hope. 3. Create tables that show how much I will spend over the long run with each type of toilet. Consider the upfront purchase, installation and monthly water costs for each toilet type. Old Toilet -5 GPF 1.28 GPF 1.0 GPF Years Cost Years Cost Years Cost $ $ $ 1 1 $ 2 2 N $ 3 3 $ n n