PVC glue fumes in pipeyste
The fumes should dissipate soon after gluing everything up. I have not experienced smelling strong fumes from the glue long after the pipe has been glued. You might get a faint odor, but it should not be strong smelling.

What you probably smelling is sewer gas. Sewer gas will build up in the pipes, and you would smell a strong odor coming from the pipe after it has been blocked off for a while. This gas is considered harmful, and is extremely flammable in concentrated amounts.

Since there is a trap, you could try filling it with water before capping it off again. The water in the trap will prevent the sewer gas from coming into your home. Wait a few hours, and remove the cap. If you don't smell fumes, then the source was most likely sewer gas.