Hi, I'm in the process of finishing my basement and I decided to install a toilet as well since there's already a drain. So when I was buying the toilet and tank over at home depot, the guy told me not to get the 6 liter (1.5 gallons) because basement toilet needs at least 13 liters (3.4 gallons) to flush? how true is this? Btw, my house is only about 5 years old. Thanks