I talked to a guy about installing one on my land today and was suprised that he said that only 2-250 gallon tanks would be enough for the system. The wife and I plan on building a house later on closer to retirement but wanted to go ahead and put one in for our 5th whel trailer. I figured go ahead and get it set up for the house later on down the line. The house that we've been looking at is about 3700 sq. ft and would have 3 1/2 bathrooms. the majority of the time it would be only us but you never know when a child is going to come back home to live and possibly bring their family with them. It just seems to me that 500 gallons is kind of small. He saying that since the soil is real sandy that it will disperse(?) quiker and better so that a larger tank will not be needed. Any thoughts?? Thanks.