I discovered the source of sewer gas in an older home... there is no trap in the basement shower. There is also a pipe from the clothes washer that runs into this drain near the top, just under the bottom of the shower. It looks like the pipe drops about 12" into a tee under the floor. I'm guessing this is a 2" pipe. The bottom of the shower is about 4" above the basement floor. It looks like everything is concrete with no access. I'm planning on replacing the old home-made concrete/tiled shower, but is there anything I can do NOW to solve the gas problem?

Plug off the shower until you can install a trap. Good luck, Tom