Hi-I had a powder room installed in an addition w a toilet w an injector pump. Initially it caused backflow into basement sink. A plumber added a check valve under bsmt sink and corrected this problem. But secondary issue is that when flushed a few times the Kitchen sink-located on main floor as is toilet w injector pump-will gurgle.
Is this a problem I should be concerned with and if so how can it be corrected- help as I am selling my home and do not want to pass on any possible issues to new buyer-
THX!

This sounds like a venting problem. I believe the plumber placed the check valve on the sink vent and not the drain. In point of fact you shouldn't have had a back up from the sink if the job went in correctly. The back up had to come from above if it got into your sink . If the back up came from drainage side it would have come up in the lowest spot, the toilet or a shower. It had to come down the vent.
This makes me wonder if the plumber didn't "fudge" a bit on the vents. You should have had two vents installed. One from the sink that could have gone up to the attic and revented back into a existing roof vent and another, a dedicated vent out the roof for the holding tank. If the installer connected the grinder pump to a house vent you would bave had a back up from there basement lavatory. A gurgle in your sink indicates a vent problem. The gurgle's caused by the sink attempting to vent through the trap instead of the vent. This occurs when the sinks vent is blocked. I would have the ejector system checked over but I wouldn't call the same people to do it until I got a independent opinion. Please keep me in the loop on this and tell me what you found out. Good luck, Tom