Official permits and inspections are very helpful in some localities and simply farces in others. Get a good plumber to come look at your installation and ask for his advice. If you call the authorities first, your basement bath may be "toast". Perhaps the plumber can correct the major problems and it will operate satisfactorily.

I strongly suggest you follow Bus Drivers advice and get a competent Plumber to look at your situation.

From the symptoms you describe there is definitely a venting problem however it may not be near as bad as you might think. A competent plumber should be able to look at the size of the room and the fixture layout and from that pretty much determine the pipe layout. In all probability all they would need to do is connect a vent to the riser behind your lavatory and extend it to the roof or perhaps tie into another existing vent, (subject to some strict rules here).

There should be absolutely no reason to tear up your floor however one word of caution. Do not let anyone talk you into installing an AAV (Studor vent) An AAV would allow air to enter your pipes to protect the trap seals, but from your description the problem is a result of hydraulic positive air pressure in the lines when you use a fixture. An AAV will let air in to prevent a vacuum from sucking the traps dray but it cannot relieve positive pressure.

I have a plumber coming this morning, so we will see what happens.

lazypup- interesting about the Studor vent- I had a plumber here a few months ago who suggested that for a sink in my new kitchen island. I have since decided not to use him since I learned he was not a master plumber.

bus driver- what do you mean about my bathroom being toast? Are you saying that it would all have to be ripped out?

Do not be too quick to dismiss your previous plumber for suggesting a AAV (Air Admittance Valve, "studor vent") for your kitchen island.

Although the Uniform Plumbing code(UPC) & International Residential Code(IRC)have radically differing views on how a kitchen island vent is to be constructed, nonetheless, both the IRC & UPC do allow an AAV for kitchen island venting.

Under the IRC all structures are required to have one "Main Vent",which must run undiminished in size from the structure "Main Drain" through the roof. After that we are permitted to install an unlimited number of AAV's.

Under the UPC they do not require a "Main Vent" but all fixture vents are required to be sized by the total DFU (Drainage fixture unit) load of all fixtures served by that vent. Under the UPC a structure is only permitted a maximum of one AAV, with the expressed written consent of the local inspecting authority, and in most cases a kitchen island is the only location where they will grant the exception.

Now what is the difference between the kitchen drain and your bathroom drain you ask?

When we have a sink on an island it is generally the only fixture attached to that line. As the water drains from the sink it pushes the air ahead of the water in the pipe. Under some circumstances this can result in a slight vacuum in the pipe behind the moving water. This partial vacuum would then result in the standing water in the trap being sucked into the pipe by siphon action and once the water has passed on down the trap is left dry, allowing sewer gas to enter the structure. In this case we install an AAV, which would permit air to enter the pipe behind the liquid flow, thus negating the suction effect.

There is a slim chance that you might resolve your problem by installing an AAV on the lavatory drain line, an when you consider the cost of installing an AAV as opposed to opening walls it might be well worth your time to try it, however I suspect you have a different problem in your bathroom.

You state that you hear a gurgling sound in the tub or lavatory when another drain is used. It is possible that the water in the gurgling trap is being sucked out, and in that case an AAV might resolve the problem, but I suspect you problem is not a result of negative pressure (the partial vacuum) but rather it result from positive pressure. As the water from one fixture flows through the pipe it pushes the air ahead, causing a slight positive air pressure. Normally that positive pressure would be pushed up and out a roof vent however if your system does not have the required roof vent as one fixture is draining it will push that air up through one of the adjacent fixture drains and out through the trap. Keep in mind that the air in the line contains sewer gas so as that air & sewer gas mix is pushed out you get the odor. The odor may seem greater at some times than others. That does not mean the sewer gas is not leaking because not all the component of sewer gas are odorous. In fact, one of the main gases that comprise sewer gas is totally odorless.

First plumber came and said that there is no venting for the shower or tub, confirmed by photos I have taked during the renovation. He thinks we will have to demo most, if not all of the room. He does not suggest an AAV, but doing it the "proper" way, with it going through the roof.

I have another one coming tomorrow, and another on Thursday, and possibly one today. Will post when I have some additional opinions.

lazypup-thanks for that very thorough explanation of AAV's. How do I know which code "trumps" the other? Will my local code possibly be different?