There is a company called "Sleuth Plumbing" who does a lot of trick pumbing (video inspection, pipe bursting, pipe lining, etc.). One of thier other tricks is odor detection. I've only used them for video inspection and pipe lining but you might give them a shout if you are in Florida.

If you are not in Florida you might do a search on "odor detection" or call sleuth and ask them if they know who does this in your area.

Jim

Here is a link that might be useful: sleuth plumbing

I see one of four potential problems here:

1.Pour about 2 quarts of water in the drain then use a flashlight and look down the drain to see if there is any standing water in the pipe? If you see standing water down in the pipe that is your trap. Hexus mentioned pouring distilled water in the drains to prevent evaporation. I can assure you that will not work because distilled water would evaporate at approximately the same rate as tap water. On the other hand, if you pour about 2oz of vegetable cooking oil in the drain it will float on top of the water and retard evaporation.

2.Examine the floor drain. If it is cast iron and appears to have a center pipe extending up to approximately 1/2" below the floor level and an outer section surrounding that pipe about 2" wide that holds water there is no trap under the drain opening. For those type of floor drains the lid has a pipe section that hangs down into that outer channel. With the lid in place water enters through an outer ring of holes into the outer ring, flows under the section of pipe extending down from the lid, then up and over the center standpipe to enter the drain. If the cap is missing or lost there is no trapping action. (In most jurisdictions we are no longer permitted to install that type of floor drains),

3. Check your furnace to see if you have ducted return air or is the air ducted into the basement then is drawn from the basement into your furnace return air duct. If this is the case you may not have sufficient return air ducting and while the furnace is running it is creating a slight negative air pressure in the basement and the sewer gas is being sucked up through the water in the traps. The solution here is to have dedicated return air ducts installed from the living space above directly to the furnace air return.

4. If you pour water in the traps and top it off with the cooking oil but you are still smelling the sewer gases your basement may be too tight to permit an adequate supply of combustion air for your furnace, water heater and laundry dryer. The code requires that we must find the manufacturers BTU rating on each appliance and add all the BTU values together to get a total BTU/hr rating for all combustion appliances. Code defines a "Confined space" as any space that has less than 50 cubic feet for each 1,000 BTU's.

By example furnaces typically range 50-200Kbtu/hr. For the purpose of illustration let us assume the furnace is 100Kbtu plus 35Kbtu for the water heater and another 35Kbtu for a laundry dryer. The total combined BTU/hr rating would then be 170Kbtu per hour. We are required 50cu.ft for each 1kbtu so it would be 50cu.ft x 170 = 8500cu.ft. Now assuming the basement has an 8ft ceiling we have 8500cu.ft / 8'= 1062.5sq.ft. In this example if the room in the basement where the furnace, water heater and dryer are located has less than 1062.5sq.ft it is a "Confined space". The end result of a confined space is that the appliances will produce a negative air pressure, resulting in improper combustion which produces high levels of carbon monoxide. In addition the slight drop in air pressure will result in sucking air down from the living space and both air and sewer gases up through the floor drains. Whenever we determine that the gas appliances are in a "Confined space" we are required to install ducting to allow additional outside air into the machinery space. (The size and placement of the air ducts is also very closely regulated by code.)

WOW, this is great information, I am going to print it all out now and do some investigating, i will get back to you on what i find. thanks so much for the time and effort you have put furth in replying to me.
the basement smelled a bit better for about 1 day so my watering the drain helps but as soon as i turn the water off it gets stinky again. i am going to research all of your suggestions now. thanks.
sue

well, after lots of sluething around my basement, i found the wall the smelled the worse. i moved everything from it hoping to find a dead something or other--nothing.

so, in tears, i go to my neighbors. they came over and we all then decided it must be a dead animal under my front porch. there used to be a skunk that lived under my porch from time to time, we tried to get rid of him but putting rocks and dirt down the hole. so we go out there, and the hole is there, we do a bit of digging, huge flies, maggets and all of a sudden--that SMELL.

so we decide it is a dead animal under my porch. now, my porch is a concrete slab on the dirt so we throw some moth balls in it and mix up a 50lb bag of cement with rocks and put that in the hole.

i am sure i will have to deal with the decaying smell for a while but i hope it goes away soon. the hole probably has a long tunnel so trying to dig under the porch is nearly impossible unless i wanted to get a construction like company out there to do it.

i am so tired. and i just realized my granite counter top has oil stains on it from making brushetta so i have to figure out how to get the stains out and get it sealed. i am getting tired of being a home owner.

sue

One of the advantages of being a country bumpkin (me) is that distinguishing between smells is a skill acquired at an early age. Sewer gas and dead animals do both smell bad, but the odors are very different. Cleaning out animal confinement areas brings one to the point that one can identify by odor the species of domestic animal that produced the manure. And we had to dispose of dead animals too.

":On the other hand, if you pour about 2oz of vegetable cooking oil in the drain it will float on top of the water and retard evaporation."

Use mineral oil from the drug store.

it will not evaporate to any degree.

All vegetable oils can go rancid.

yea..but cooking oil is not prohibited by EPA

the smell is losing it's effect--animal must be decaying--now i too will have the nose to know if it is a sewer smell or that of a dead animal. ugh. ok, back to spring cleaning.
thanks again, you are all cool

"yea..but cooking oil is not prohibited by EPA"

Neither is food/medical grade mineral oil.