Been spending a fair amount of time since Friday working on a really-don't-want-to-learn-this item. A 4" sewer pipe in our leach field bit the dust. This is solid thinwall, not the perforated type.
Best I can tell, the original fault occurred a while back, when it seemed we had a small depression/sinkhole pop up. It became obvious that the ground was damp there, and things were a bit smelly - clearly something not right.
After a .... load of digging and tracing back, it looks like years ago there was a fail in an original 40 yo pipe, replaced with a newer piece running diagonally over a stripped down distribution box; the stripped box had the base pan and cap cover, while the part with the connection fittings was removed. New pipe ran over the top of the cover. Old pipes that used to go into the box had been cleanly cut, just at the boundary of the box.
The box innards weren't filled, creating a 6-1/2" gap below the cover (to the bottom of the pan). The cover failed, ground caved downward. Pipe on top of the cover was fragmented into tiny shards, impulse force downwards, though the fail started with the pipe trying to "bend" around the lip of the tub. Pipe at the lip flexed upwards, and the part outside the box had an equal and opposite reaction pushing downwards. The pipe is not built for that kind of shock, pancaked (rip open along top center, splaying to the sides).
The fail appears to all be on the inlet side. The outlet had another new piece of pipe in parallel with one of the old, cut, pipes, with a 90 degree elbow to the new piece crossing the cap. The elbow hadn't been glued, could swivel freely. Both hub connections on the elbow had cracks, but the outgoing pipe appears to be fine (no deformation or cracks).
I think I've traced the ripped inlet pipe beyond the fault, to where it's pretty clean again. Super tight to work in, right next to a chain link fence. With any luck tomorrow I'll carefully clear a bit more soil from around it, be able to hacksaw a clean joint and attach a new piece of thinwall.
For want of whoever did the original work bothering to fill the empty box with gravel, or even soil, decades later I get to fix the mess [emoji3]
(On the plus side, the weather's been cool enough the last few days during the bulk of the digging. I'm getting too old to want to do this much digging and playing with leach field stuff when it's hot and humid [emoji16])
had to drill and tap a few holes in a 3/8" thick aluminum plate for 8-32 screw/"bolt"... Aluminum is one of the more dificult metals to drill and tap being that its soft and "gummy" ( copper is another)... anyway, I ran out of WD 40 ( which is use to lubricate the aluminum for the tapping process)... didnt want to go to Walmart for WD40 so Im looking around to see what I can use as a substitute... and I saw some copper based Never Seize sitting on the shelf of my reloading station... and I said to myself... " Self, whatchathink about copper nerever sieze as a lubricant?? Self sat there a moment and finally said "dont know, lets find out"... So I grabbed the Copper based Never Seize and dabbed the tip of the tap into it an proceeded to tap the hole... it started rather easily, it began to cut into the plate and I and Self began to wonder when its going to start getting "grabby"... it never did, it just kept on tapping the hole out, no back tracking no tightning of the threads on the cuttings. Self just kept on going at it, I began to become worried that Self was going to snap the tap off in the hole like I did earlier this week... anyway Self did a wonderful job now I can take the credit for it... if it messed up all I could do is blame my Self... 
