I'm getting a 'sewer' smell being picked up by my HVAC unit since the new (larger) unit was installed.
ONLY after taking a shower in the guest bathroom.

A new AC return was installed just outside the mech area.

Th diagram shows the way the SS is currently configured.

I'm thinking the ejector pump drain being the first and highest run off the outpath could be channeling the septic sewer gasses away from the main before it can travel all the way to the far side of the house to hit the vent.
Then the new HVAC return could be pulling the gas somehow in from the pump pit.
The E.P lid is secure and I have already coated all joining surfaces with Plumber's Teflon Pipe Dope to seal them.

There are AAVs on the drains for the other two bathrooms and the kitchen.

I've checked all the pipes in the crawl space, and find no damaged pipe or loose fittings.

I'm considering moving the Ejector pump connect further back from the outter wall, and using that existing 45* fitting for a new vent to the roof

Does this sound correct or logical?

 

Why not just dig a new out house?

 

your diagram looks ok. BUT, it is going to depend on how you ejector pump is connected. I am assuming that you shower runs into a pit (sump) and the ejector pump turns on after a certain fluid level is reached within the sump.

Right now it looks as though you have a horizontal 'wet' vent. IIRC the maximum length for this scenario is 2 or 3 feet per inch of diameter of drain line. A 4" horizontal drain can be used for a vent if it is within +/- 10 feet of the drain it is venting. There is also a limitation on the distance of the 4" pipe to it's main vent as well. Check the code, but horizontal wet vents are a LAST resort in almost all cases. They are very tricky and very unforgiving.

The vent needs to be located close to where the drain off the ejection pump reaches it's highest point, and on the down hill side. There need to be a trap between the vent, and the ejector pump, and depending upon the design of your ejector pump, you may need a trap loop which vents both sides of the trap. If your ejection pump has a check valve, then water can not fall back into the sump, which can cause a siphon. If it has a check valve, then a single trap will suffice.

The location of the trap can be in a number of different places, depending on your plumbing design. The trap needs to be accessible (for cleaning) and within 4' of the vent. The vent needs to be on the drain side of the trap, not the feed side. There is only one shower on this drain so 1 1/2 vent on a 1 1/2 or 2" drain is sufficient. You can tie this new vent into you existing vent but it has to be 4' above the highest fixture the vent is servicing and your main vent line must be large enough to service this additional vent load. This vent can run on a horizontal plane, but it must have a minimum of 1/8"/foot of slope down towards the drain, or up to the roof, however you want to look at it. Your vents must all be able to drain away from the venting point. You also have to run the vent vertical to a height of 4' above any fixture that vent is servicing before changing direction.

Not sure if this answered your question, but if you pipes are intact, the only way to get sewer gases into living areas is by the lack of a trap, or improperly vented drains, or both, which can cause a siphon.

You may not need to relocate the pump, you may ( most likely) just need to add a vent. Just remember that vents not only allow water to drain freely, they also stop traps from drying up do to a siphon.

 

Thanks, LOTS of good information.
We have a great, diverse membership here that allows us access to a HUGE knowledge base, and never disappoints.

(Well as long as we make exceptions for my fellow admins)

A couple of observations:
I noticed there is no AAV on the ejector pump discharge.
Should there be?

Yes it is what you called a 'wet vent'.
The run is approx 60 feet from where the outter wall /ejector pump connects to where the the vent stack goes vertical and is 3" pvc .

 

Another thing to consider is an AAV is a one way vent. I believe a pump pit must have at least one real vent to function properly.

 

Actually that is good. now we know that that is your problem. you are siphoning the water out of a trap (somewhere) and opening up the living area to sewer gas. Obvious I know, but we now have the culprit (very important).

You need to find the trap that is being siphoned out. It almost has to be the bathroom, but I have seen weirder things happen.

We have to look at a couple of things. Your discharge line from your pump rises up to the drain line, if there is not a check valve in the pump, the discharge line will siphon the system when the pump shuts off (water falling back down into sump).

Two different designs required in each situation.

No check valve = independent vent for sump and pump discharge line direct to atmosphere. Can't use an AAV here there will be push/pull on the vent. Can't tie into main stack either. PITA!!! But if you really want to do it right, this is the way to do it. No moving parts in the plumbing system = peace of mind.

Yes Check Valve = no need to vent pump discharge line (no water falling). Vent sump, and vent and trap drain line = problem solved.

You can vent the sump with an AAV as it will most likely remain dry anyway, but you have to place the AAV above the top of the pump discharge line. Then trap and vent the drain line. The drain vent can tie into main stack as the living area is isolated because it is BEHIND a trap. Or you can just run a separate vent to the roof, depends on the situation. I would run an independent vent, but I do not like AAV's. They will rust out and fail eventually.

When locating vents: they must be BEHIND or AFTER a trap. If you put the vent in FRONT or BEFORE the trap, you have nullified the trap, and will allow sewer gas to enter.

From the drain source: vents always run UP hill and drains always run DOWN hill. No exceptions, ever.

Don't forget to locate clean-outs. Prior to every 90* change in direction no matter how it occurs ( 2 - 45* = 90* ). Use long 90*'s also. Makes your life easy when you have to go fishing, and you will.

I ALWAYS go to 2" drain lines as fast as possible, and use a minimum 1 1/2" vent lines, but generally go to 2" as soon as possible. Remember, future expansion may require bigger vent so put it in now. Clean-out's can be strategically located on vents as well, so plan for the future plug. Put a street Y with a plug at your AAV. If it backs up and you have to wash out debris it makes it very easy. Clean outs must have 3' of clearance to the opening to gain entrance and insert clean out tools. Choose their location wisely. It also helps to have power close by, but not directly below them (Duhh!!!) Also, if you have a long run you may need an intermediate clean out. The plug (on all clean-outs) must be pointing up at a minimum of 45* (straight up is best but not always possible) to reduce turbulence in the drain line, so it does not create a plug by gathering debris.

For reference Home Depot has a spiral bound, laminated basic plumbing code book. It goes over the nitty gritty of plumbing and vents and is only about 15 or so pages. It is a great reference and should be more than adequate to give you the theory and basic requirements to design your system. They also have one for electrical work in the same format. Very good reference material and more than adequate for your needs in this situation.

BTW, I am not a plumber by trade, but like you have had to investigate and figure out systems that were not functioning properly. I have designed (and redesigned) quite a few systems that have not only passed inspection, but far exceeded requirements. When I owned my construction company we called it code plus and in my opinion it is the only way to design and ensure future requirements were met with limited design intervention...

 

I think I might have found the trouble spot............

When the GeoThermal system was installed, the LARGE return duct from the front hallway was supposed to be rerouted to the attic to be picked up by the rest of the newly installed returns, and the old duct was to be blocked.
They connected the old duct to the new system right beside the ejector pump..................and left the zip tie securing it to the return plenum so loose that I was able to pull 14" of slack out of the tie.
Couple that with blocking the basement return, and we have NO septic stench after Wifey used the shower this afternoon.

Not sure which one solved the issue YET........ but I'm going to have the HVAC company MOVE the basement return grill farther away from the Mechanical area.

 

All great advise, but I still say my suggestion is the simplest.