I needed save space so I thought a trough waterer would work well.
Step 1: PVC Rain Barrel
I also installed a chain to keep the barrel from falling over when full.
NOTE: Use the fast curing 5200 marine adhesive. The normal stuff takes a full week to cure and waiting gets really old!
Step 2: Gutter Connection
I also included an overflow leg by using a tee and a 90 deg elbow so I can see if the system if full. If the system is full or its raining so hard that the rain barrel can't keep up, the excess water flows over the weir and down the gutter like it normally would.
I used the following 3/4" PVC parts:
(5) Short sections of 3/4" PVC
(2) 90 deg elbows
(1) End cap