Gray tank questions

[Sundown08]

Hi Everyone:

We own a 2014 Big Sky 379RL. The specs state that we have a 93 gallon capacity on our grays tanks. I have two pull valves for the gray tanks. I am assuming one for galley and one for the bathroom. Is the gray tank capacity split between two tanks? If so are they split 50/50? If so 46.5 gallons per tank?

I have one other question. We live full time in an RV Park. Prior to getting the Big Sky we had a Class A MH. We used to always leave the gray tank open. When we do this with Big Sky we can smell a bad sewer odor. As soon as we close the Gray tanks the order goes away. Never had this issue with the MH. Could the smell from the sewer be coming through the vents for the Gray tanks? The smell is in the air around the trailer not underneath or close to the trailer. Its when you get 20 or 30 feet from the front area of the trailer the you can notice the smell.

Your comments and suggestions would be very much appreciated.

Regards,

Steve

[kdeiss]

Not familiar with your Model all Montana's are the Same Two Gray tanks one for Shower and Bath Room Sink the other for the Galley. Their should be a pull for the bath room between the tires. the other gray and black in the conveyance center.
I am sure someone with your model be along

[DQDick]

Never actually measured, but I think ours are about equal. The sewer smell is coming from the fact that your tanks are open to the sewer and the vent pipe is open to the air. Many MH's have this same issue. If your's didn't it had a P trap on the the sewer line in the coach somewhere. The simple solution is to make a little P trap in your sewer line on the way to the sewer opening.

[Sundown08]

Hi Dick and Ken:

Thanks for the replies. Very helpful! I am going to try the P Trap in the sewer line. Makes total sense!

Regards,

Steve

[jcurtis934]

The galley grey tank is 40 gallons, so that leaves the 53 gal approx for the shower grey. Our unit has the same specs and I have had the bottom totally off to see the tanks. Black and grey for bathroom are the same size tanks...galley is smaller. You can bank on this answer. John

[Sundown08]

Thanks for the info John!

[rohrmann]

Ours is also the same, black and bath gray are the same size, 53 gallons, so the galley should be 40 gallons. When you leave the gray valve open, your rig is now a vent for the entire RV park sewer system, as there is not a P-trap in the sewer drain plumbing of your rig. It's much better to just drain the gray and galley tanks every couple of days instead of having to smell sewer gas all the time.

[bncinwv]

The P-trap can be easily made with your sewer connector line. If you use a support for the hose, stop the support short of the sewer connection itself and let the black flex line sag at the end to form it's own p-trap. We leave the galley tank open all the time since our washer and dishwasher drain to it. We prefer to leave the gray (sink/shower) tank closed to use it for flush water after emptying the black tank.
Bingo

[Artemus Gordon]

There is a "safety vent valve", which can get stuck, it goes out from time to time. You must replace it. They are found in newer RVs, motorhomes etc. Mine are located under kitchen sink and bathroom sink. They are designed with a spring, that makes them open and close with presure and prevent water from entering pipe and release air. I think some people call them " Air admittance valve" "air check valve, or check valve"? These small troublesome valves, are available at most RV dealers and come in different sizes. Note: installation is easy if you can get to them. Mine have each been replaced 2xs since 2012. Gray tanks can smell as bad as black, given time. They install "inline" so you might have to cut and replace with pipe cement! My first one went out in three months. Note: on my 3750 the valve for kitchen vent is odd ball size, hard to replace. You need to find yours, remove it and take it into be sized. Save you couple trips to RV store! You should "never..ever smell that tank" if valve is not stuck open!

[Sundown08]

Hi Everyone:

Thank you all so much for help and advice!

Best regards,

Steve

[shovelhead86]

i like to drain by opening the Black tank first and after a few minutes open the full gray tank. it tends to flush the black tank and the hose.

[DQDick]

Those under sink venting parts do fail from time to time, but when they do the sewer smell is in the rig not outside of it.