I have a commercial building that has concrete floors and is flat on the ground. There is a septic tank that is quite old. When we have 2-3 inch rains, one of the two commodes (the one closest to the septic tank line) backs up with clear water and the commode actually overflows into the floor. Would having the septic tank pumped out helped or would this require either installing a new septic tank or connecting to city sewer (which is now available?). Please explain why this happens if at all possible.

Thanks.

Its all up to your pocket book but I'd get a price to connect to the city sewer. You say the septic is old and it appears the field is water logged but you need to tell us if there are other plumbing fixtures in the building at a higher level of elevation than this toilet lip, like a second floor or washing machine

It is all on the same level with only 2 commodes and 2 sinks as the only plumbing involved, and these are side by side in the same general area.

Unless the rim of the toilet is below the level of the sewage inside the tank this should not be possible unless some other fixture is discharging at the time of the over flow, water doesn't run uphill. Is it possible that the toilet is lower than the top of the septic tank?

No, the toilet is located on the concrete surface at ground level. The septic tank is in the ground outside of the building significantly lower than this toilet. Someone had made mention that there could be a crack in the line and this could be ground water that is backing up, but what is so strange is that it is always clear water that backs up and runs over, it is never muddy or dirty sewage type water.

A crack is possible but water would still have to have head pressure to rise up to the top of the toilet's rim. Ground water has no head pressure