I have read that it might be related to the vent... I do have a sewage smell, periodically in the room where the pipes go into the floor (is that the vent or is the vent a separate pipe. ) I think I found the crack... it is right by the floor... I put some flexible putty to temporarily plug the crack but haven't fully fixed it. I bought "mightly putty" that has an activator that says it bonds to almost any surface.

I also have had problems with the washer water coming up in the toilet but hope that has been fixed with a main sewer drain replacement... but still over the low water level in the toilet problem" Perhaps they are unrelated.

How high is the water level in the tank compared to the overflow tube?

Hi,

What could be happening is that you have improper venting and with that said, it results in a siphoning of trap seals. Because lack of proper venting you are not getting the equal atmospheric pressure in your drain lines. When liquid waste and solids are draining, air is pushing and pulling waste in your pipes and it is creating pressure differential in the pipes. The other thing is some states use traps that are called S-Traps which are not legal with states that adopt upc codes because of trap seals are being siphoned with pressure change in venting system.

For example, in a multiple story building, waste flowing vertically travels 15' per second and creating pressures downstream and could blow a trap seals out of the fixtures , etc. So to maintain equal pressure in venting a yoke vent is installed or install proper venting. It is plumbing experience.

Here in California with the upc and cpc codes are always being studied and improved because of this issues.

I WOULD SUGGEST LOOKING FOR A PLUMBER THAT IS KNOWLEDGEABLE

not all tampons are made to break down very easily and could clog your toilet I have had it happen to me my suggestion is when your girlfriend gose and buys tampons (tampax recamended) tell her to look on the back of the box and make sure it says biodegradable on it..,. http://www.tampax.com/en-US/products/tampax-flushable.aspx?gclid=CJLv2riMsKUCFYHc4Aodk0PWYg

the pipes go into the floor
This bothers me. Do the pipes go from the trap down into the floor or do they go into the wall? (see images) Let me know, Tom