Mystery Plumbing situation with slab on grade rental stoppage.
From the 4" main line outside I guess a 3" or possibly 4" sewer pipe extends into the house -about 4ft to a minimal size ptrap shower tub drain (1.25 " dia possibly 1.5") the house sewer pipe extends further about 4ft and connect to a toilet and 6' further onto a sink. Either before or after that there is a 4" diameter asbestos vertical roof vent through the roof.
Suddenly - instantly (the tenants, with a 2 year old, says) the toilet failed to drain and some of the brown/black water came up through the shower tub drain but not much. The sink had no similar problems. (The kitchen sink is on a different circuit.)
Neither would drain! But the sink at the far end had no drain problems. And the toilet flush full of water would have different water levels by about 18 inches after each effort!
First I used a toilet auger (has a 36" reach) - that changed nothing. Then I ran a snake about 6 ft into the tub overflow hole - also change nothing. With great difficulty same thing in the toilet.
Water was at two levels and still not draining.
As a desperation move I climbed onto the roof and inserted a garden hose into the vent pipe and gave it a full blast of 90 psi water. This must have scared the s*** out of everything because suddenly everything drained properly! This was no doubt constructed to minimum UPC standards near Los Angeles years ago.
To me - clearly some kind of foreign object put into the toilet - by some human. But what - with the two water levels? The main line had no problems - checked first thing. Could it have been years of accumulation of sewer debris that suddenly got loose and caused this?
Is there a reasonable explanation for any of this and the persistent two water levels? Some of the really brilliant practical minds are known to frequent this news group.
Thanks in advance, mic