Engineer-Designed Rain Barrel System: 7-Barrel Setup with Detailed Plumbing

Reader Grant P., an engineer, shares his refined rain barrel design—seven barrels installed at his home, all functioning flawlessly. He admits he may have "made it too hard," but his engineering background drove the precision.

System Overview

All parts sourced from home improvement centers (Lowe's). Components span three store sections: plumbing fittings, roofing/gutter, and outdoor garden (corrugated drain pipe).

Key Design Features

Inlet & Overflow Design

• Two flex gutter pipes: One from house downspout (cut section) to tank inlet; second from tank overflow to ground drain pipe.
• Critical rule: All gutter interfaces must transition from smaller to larger fittings in flow direction (or use watertight fittings).
• Tank inlet: Square hole in tank top fitted with a water plant pot (mesh box) from Lowe's water garden section. Allows arm access for internal work.
• Inlet seal: Rubber sheet over mesh box with hole for flex downspout, or roof vent flashing (rubber gasket cut to fit flex pipe) for a clean, screened entry.
• Overflow outlet: Rectangular hole near tank top fitted with sheet metal gutter flange, sealed with gutter sealer (tested 4 types—this worked best for mechanical strength + seal). Flex pipe screwed to flange, sealed, then inserted into ground drain pipe.

Spigot Installation

• 3/4-inch threaded brass ball-valve hose bib (full flow, better than knob-style which restricts flow—important if connecting a pump).
• Drilled hole in tank, self-tapped threads with the bib (pause/back up occasionally).
• Removed bib, added steel washer + gutter sealer on threads, reinstalled (leave 1 thread loose for sealer room).
• Optional: Flange nut on inside (from electrical conduit section) for extra strength—Grant skipped this with no issues on thick-walled barrels.

Multi-Tank Connection

• 2-inch PVC Schedule 40 male-thread-to-female-solvent adapters at bottom sides of tanks.
• Connect with 2" PVC (flex PVC preferred, rigid Schedule 40 works).
• Drill holes with hole saw, cut threads using 2" steel pipe with cap for leverage.
• Seal adapter threads with gutter sealer, solvent-glue PVC after sealer cures.
• Secondary tanks need venting—screen flap over factory bung hole works.
• Example: 80-gal main tank + two 60-gal food-grade barrels, with 2" ball valve on main to isolate supplementary tanks.

This comprehensive guide enables serious DIYers to build a professional-grade, expandable rainwater harvesting system.