Just as the failure of my biogas digester led to the construction of my initial continuous compost tea bin, the failure of the latter led me to start thinking of ways to improve it. The first version, while it did indeed meet the goal of creating a nutrient-rich watering solution using kitchen scraps, yard waste, and rain water, failed in a number of ways. First, the outer trough, which was open to the air and which had its drain located higher than I'd have liked, allowed for standing water, which in turn bred mosquitoes. Second, the weight of it - especially after I'd added a few months' worth of compost to it - collapsed its stand. Third, cutting apart a plastic 55-gallon drum really compromises its structural integrity. Fourth, the bolted-and-silicone'd method of sealing the two halves of the outer trough started leaking after a few months, rendering it useless.
But hey, I used what I had on hand. And I learned from the process.
I had some ideas about building an improved version using smaller barrels cut to fit tighter together or maybe some inexpensive plastic totes, but while kicking around some five-gallon pails I had behind my garage, it occurred to me to use them instead. After all, they're designed to fit within each other without gaps - eliminating the mosquito problem from the get-go - they're inexpensive and plentiful, they'll easily accept lids, and they come with handles, making them easily portable (for you apartment gardeners). Oh, and I already have them.
All I needed to do was drill a few holes, make a few cuts, and I had a much better - albeit lower capacity - continuous compost tea bin.
Step 1: Step 1: Set Up the Outer "trough"
The lowermost bucket will be the one that collects all the compost tea as it drains out of the actual compost bucket and then funnels it toward your irrigation system or collection bucket.
I salvaged the bulkhead fitting and boiler drain from the first version of the tea bin and only needed to drill a 1-1/2-inch hole as far down the side of the bucket I could go without hitting the floor of the bucket. Why not mount the bulkhead fitting in the floor of the bucket? Because I've never had good luck drilling holes in the bottoms of buckets - they always seem brittle there for some reason.
Make sure to get the bulkhead fitting as tight as possible and then tighten it some more. While testing, it seemed to leak until I'd applied monster torque to the fitting.
Tip: When drilling the hole - especially when using a holesaw without a center arbor - try running the drill in reverse. Doing so will take a little longer, but it'll also keep the holesaw from skipping around.
Step 2: Step 2: Set Up the Inner "trough"
The uppermost bucket will be the one in which kitchen scraps and yard waste are dumped and in which rain water will enter. Simply drill a few small drain holes - I believe I used a 3/8-inch bit - around the perimeter of the bottom of the bucket. The holes should be large enough to provide ample drainage but also small enough to keep the compost from escaping with the tea.
Step 3: Step 3: Make a Spacer
I discovered through testing that putting the inner trough directly inside the outer trough didn't drain the tea all that well - the holes in the inner trough were flush against the walls of the outer trough. The inner trough would drain eventually, but over the course of days, if not weeks. If you want a slow trickle of tea, then by all means skip this step.
To speed up the drainage of the inner trough, I cut a third bucket to sit between the inner and outer troughs. The cut had to be high enough to clear the holes in the inner trough and low enough to provide a good fit inside the outer trough.
By adding the spacer, the empty inner trough now drains in a matter of minutes. Should I decide in the future I want a slower trickle, I can just remove the spacer. Or I can regulate drainage speed with the boiler valve.
Step 4: Step 4: Assemble and Use
Assembly is simply a matter of stacking the inner trough, the spacer, and the outer trough, then either hooking up the boiler valve to your irrigation system or positioning the bin above a collector.
To keep the compost from draining out with the tea, I've lined the inner trough with small stones. If you've foregone the intermediate spacer, the stones probably aren't necessary.
As with the first version, I'm using a food processor to grind up my kitchen waste before I add it to the inner trough. I'm also emptying my basement dehumidifier into the bin and I've positioned the bin to catch rainwater off my garage roof.