Totes are pretty easy to come by. Single-use food grade totes run a couple-three hundred dollars around here with the port essentially right next door, but often you can find them for $50-75, which is what happened with this one. $75 and missing a cap- the caps cost about $10 new. In the end I didn't even use the caps.
There is already a drain at the bottom, on one side. The top opening is about 6" and the bottom is (I think 3") with a valve. The valve is kind of the issue, when the gate inside the valve is open, it's still not an unobstructed opening. The chunkiness of the effluent just doesn't drain super efficiently. In a purpose-built setup, this wouldn't be as much of a problem, but I'm dealing with an experimental, improvised rig that is meant to be as cheap and DIY as possible. I don't have any equipment for welding HDPE, so I used bulkhead fittings where necessary.
The 4" PVC top-feed mechanism was a definite compromise, but the 4" to 6" rubber boot adapter made it feasible and cost-effective to seal it.
Top feeding is ergonomically inconvenient: too high off the ground, requires me to stand on a bucket or something of similar size. It makes a ram or plunger necessary to get the feed stock fully submerged and to clear the feed pipe. I had to be somewhat careful with the plunger because the top plastic is largely unsupported and flexes- had to be careful not to pull the rubber adapter loose. You're pushing directly downward against the buoyancy of the feed stock, and you're getting a few percent of gas from the effluent directly below the feed tube escaping directly upward.
Ideally, I would not top-feed, but rather make a low, side-entry 45 degree angled chute to feed it. This would also facilitate stirring, I think. I was looking for a 45 degree bulkhead fitting of reasonable size, but it is amazing how expensive large size plumbing fittings are. A 45 degree angle side-feed chute could have the feed pipe cut longer on the bottom, so almost zero gas bubbles up the tube.
Then the caps with the threaded fittings would be very convenient. I have a holding tank/RV sump pump that could be used for stirring, with some pipe threaded through the top cap to dump back into the main reservoir and another bulkhead fitting down low to draw from the main tank.
One of the benefits of the totes is the cage and pallet built around the reservoir. This also, however, limits access to bottom and side to a certain size by the grid openings of the cage. Without the cage/pallet, moving the thing would be very difficult and prone to breakage. Stacking would be impossible. My plan was to eventually have a second tote stacked on top of the first and plumbed together for gas collection and potentially a primary acidification stage.
The sludge that came out when I drained the liquid was clearly good quality organic compost fertilizer- it smelled earthy but not unpleasant, was a good dark earth color with lots of fibrous organic material in it to provide good soil structure/tilth. Mind you, there was a high percentage of very rank/sour smelling dog shit in there, but it was completely undetectable when it came out after several months in the digester. There was no detectable distinctive olfactory influence of any of the individual feed stock- fruit, feces, what-have-you.
I don't have any place at my new house to continue these experiments, so I'm going to store the rig at a friend's country place for the time being.
I have requested that the thread be re-opened, so I can copy this conversation out into the public forum.