Has anyone offered full service contracts to cover plumbing just like is done with HVAC? If so, how would you determine how much money you would need to charge and still be profitable. I have customers that are interested but I'm not sure how to approach this. What I come up with is just inspecting their accessible plumbing, for a fee, and making recommendations on repairs needed. The fee would also include an annual flush of water heaters and cleaning of grease traps, if applicable. Trying to come up with a price for full coverage seems to be nearly impossible as you can't predict how abusive the customers can be with the plumbing in general.