Had a home inspection on a house my mother in law is planning on buying and had a couple of issues, all having to do with plumbing. The house which is a high ranch is located in Suffolk County, NY.

*Can a Fernco formed Elbow be used to attached the vertical from the trap to the horizontal into the wall stub?

*In the bathroom and kitchen the stub out from the wall is very low, to the point that it is just above the bottom of the cabinet. The traps are not p-traps but if you can imagine an "s" with the fernco elbow that turns the pipe back into the wall. Does any one see a problem with this setup?

*The previous homeowner put in a stand up shower in the downstairs and tied it into a drywell in his back yard, it does not attach to the main waste line. Even worse is when you run the shower for about five minutes it backs up into shower base. After 30 minutes the water still did not go down?

*When you run all the plumbing in the house at once, the toilet downstairs begins to bubble and gurp and the water rises to the brim. (When we got there the water level was very low in the toilet. After 30 minutes, the water level went back to the low level.

*The previous homeowner has a kitchen sink "tee"ed into what I beleive is called the house fresh air vent. Is that legal? (Is this considered a wet vent? And will it work or will it be trouble in the future)
From what is seen, the upstairs remodel was done with PVC and the piping under the slab appears to be CI.

Help should we run or stay?