This is scaring me and I can't sleep.
This forum is better than a megadose of caffeine. After reading some of these threads I can't sleep. Putting ABS glue on a cast-iron and neoprene joint is some scary stuff. Who's concoction was this?
I would imagine several bad things can happen. First, a leak in a cast-iron fitting will heal itself usually in a few hours by the natural reaction of rusting. Two bad things could happen.
1) The glue will inhibits the rusting of the pipe and lengthen the time the pipe leaks.
2) The glue may soften the neoprene and make the joint loose. The glue may cause the pipe to slip out of the fitting and kill someone or come apart underneath a house or inside a wall after the job is finished.
I've heard of plumbers adding salt to the water when they fill iron pipes for a test. Bring bags and bags of water softener salt. In a few hours even a large leak will heal itself.
Another real cool way to stop a leak in any type of drain pipe is with powdered laundry detergent. We do this when we have a small leak in a kitchen drain, trap, or a brass pop-up. Mix powdered laundry detergent with water until it is as thick as a thin milk shake. Pour the mix down a drain and don't run any water for about 12 hours. Walllllah! The leak is repaired.
Of course, I'm sure everyone knows about using a flare to seal leaks in gas piping. We had a plumber who used Seal N Air to seal a gas pipe for a test. The Seal N Air liquified and settled in the lowest portion of the system. The new homeowner moves in the house and has no pressure so we had to use a high-volume of air to blow our the liquid. A regular air compressor hose would not do the job because the air would blow over the top of the liquid. We had to us an air compressor with a 1 inch outlet that was hard to find so we rented a huge jackhammer compressor
The Glue? Scary stuff!
Its almost 12 pm. I'm tired of flapping my lips. See you tomorrow night. Same time. Same place.