Older homes in our area often have a functioning forced air furnace with ducts for all 1st floor rooms but gravity registers (basically holes-with-grills through the 1st fl ceiling/2nd fl floor) for the 2nd floor.  

Gravity flow sewer is always the best option .Good luck

No matter what they say reply, "I'm sorry sir, given the gravity of the situation I can't make statements without the advice of counsel."

I use aweber as well, but I use Gravity Forms to build my contact forms.  

In 1" pipe, you should easily have a flow rate between 3.4 and 3.8 ft/second at gravity feed (far less pressure).  

Sometimes it is very difficult or impossible to move sewer lines without an entire replumb of the house, because it works on gravity.

I am about to replace a 1950 gravity gas heater with a modern unit, add c/a and do a little basement duct work to a unit all for $5,800.Around here (Delaware County, PA - near Phila), a "3Br, 1Ba, unfinished basement and no c/a" is the "base unit" for the row homes I buy. 

The grain would gravity flow down a chute into a feed cart to be taken over to the grinder or be bagged for cattle feed.  

Why Multifamily Values Will Continue to Defy Gravity (multihousingnews.com)

Even with power outages you will always have heat.That's only true if you have a gravity system.