I have a question regarding the waste line for a new sump pump. I have to drain the water into my home's sewer line (I know I'm not supposed to do this but I have no choice). My washing machine waste line (with its p-trap) is installed between the sump pump and the main sewer stack. I can have the pipe from the sump pump come up out of the pit, ell toward the wall, then ell toward the stack. However, I need to know whether to run the line in the wall just above or below my washer's drain pipe (either at around 4 feet high or about 5-6 inches high). Is there any preference one way or the other for how to do this? My preference would be to install it below the washing machine line (so I don't have a 4 foot pipe sticking out of my sump pit) but I don't know if there's a minimum length allowed or preferred between the floor and where the sump pipe would connect with the stack (it would probably be around 5-6 inches above the ground). Any help would be greatly appreciated.

If I understand your question correctly you want to discharge your sump pump into a sewer stack which already has your washing machine discharging into it. If this is the case I strongly recommend that the sump pump discharge enters the stack above the washing machine connection. This way you will avoid having to rely on a non-return valve to prevent the washing machine possibly back feeding to the sump, furthermore, depending on pipe length & diameter vs sump volume, you may be able to install the sump pump without the need for a non-return valve - which has advantages in its own right. Call if you require additional detail.
Mike G

Don't run the sump pump into the sanitary sewer stack.
If you are on City sewers it is likely breaking a by-law or two.
The fines are going up quite a bit for a hook up like this. It also contributes to overloading the main sewer lines and causes problems downstream.
Your insurance can and will deny a claim if your sewer backs up and your basement floods from the sump pump discharging into the sanitary sewer.
Why can't you discharge the sump outside or to a storm sewer?

I'm using a sump pump to remove water from a washing machine and nearby sink. The only exit point is 7' in the basement rafters. This access point is the kitchen sink drian line that leads to the main stack. It's working well, but it has recently started making the kitchen sink gargle when pump it activeated.

Is this a postive/ negative air flow problem or did our check valve fail?