Calling all Plumbers - What's bomb proof and leak proof?

[Brandt Tingen]

I have a tenant that is using 50 - 600 gallons of water per day.  Their fixtures leak occasionally I bought the place with cheap stuff installed.  The toilets always leak.  My question is, what are the most bomb proof toilet guts (flapper & valve) and kitchen sink faucets?  I am open to commercial grade equipment, if I have to invest more up front to stop the leaks that is fine.  The tenants are Section so they are home all day.