Parts of an Aboveground Gravity Polyethylene Cistern with Underground Inflow
A) Rainhead screen: 1/8” screen mesh catches leaves and other roof debris, screen slopes at a 45 degree angle so that debris falls away.
B) First flush diverter (optional): Wall-mounted pipe sized to catch the dirtiest water- the first 1% of roof runoff at the start of each storm.
C) First flush end cap: Pipe ends at elbow with threaded cleanout cap and an irrigation tube run to vegetation nearby to slowly empty first flush pipe after storms.
D) Inflow pipe: Rainfall enters either directly from rainhead screen or after first flush diverter is filled. Typical pipe is painted plastic and sized based on expected rainwater flow calculated from roof area.
E) Observation port and imbedded vent: Threaded 16” diameter cap, usually closed, provides easy visual access to your stored rainwater. Vent ensures airflow and prevents vacuum effect in heavy rain.
F) Polyethylene tank: Fabricated from high density ¼” plastic, this tank does not require a concrete foundation and can be set on any compact, level surface. For extra height and gravity pressure, the tank can be placed on a brick foundation.
G) Spigot: A full-port (3/4” opening) ensures maximum gravity pressure. The supply line can also be extended to provide spigots in various parts of the yard, or to a pump for greater pressure/ longer distances.
H) Overflow pipe: ABS pipe directs water away when the tank is full during a storm.
I) Back water valve: On the end of the overflow pipe, this one-way flap valve ensures that water can exit but nothing can enter the tank.
J) Mulched, vegetated basin (optional): Overflow should be used as a resource, and directed to an area with the capacity to accept predicted cistern overflow and native plants to use it efficiently.