Retrofit grey tank mod

uwe · 10-27-2003, 05:53 PM

This weekend, while working on the Airstream, I suddenly realized why my huge looking add on grey tank would "fill up" so quickly...duh!
It has 2 lines connected to it, one from the streetside coming from the galley sink, and one from aft, coming from the shower/bathroom sink. The one from aft also doubles partially as the drain, the smaller dump valve tees off from this line.
Both lines go in the bottom of the tank, the shower line a bit lower than the one entering from the side.
So I went searching for the vent connection, and lo and behold, there is none! So, once the water level goes up to the top of the inlets, it's finished! No place for the trapped air to escape. It looks like a 30 gallon tank, and all the while I was getting frustrated by how quickly it would "fill up".
So next weekend I will drop the tank and see about getting a vent tube connected to one of the roof vents. I believe this will make a huge difference in the capacity and useability of this added on grey tank.
If anyone has any suggestions on how to add a vent line to the top of the tank, which is hard plastic, then I would be greatful. ( size/dia, type of hose/ type of fitting etc)

smily · 10-27-2003, 07:10 PM

I concur that you may need vent pipe but air will always find its way to the top even if it has to "burp" back into sink or shower.

My soveriegn with 35 gal grey tank will fill up very quickly if you are not turning the water off while you lather. (Military bath).

If my wife and I take a typical shower and not turn off the water during lather the grey tank will fill up after about three or four showers. The water will back up into shower.

So I do not know if I would go through the rigomors (is that a word?) of cutting a vent pipe into grey tank.

good luck with your challenges,
Smily

uwe · 10-27-2003, 08:19 PM

It's a retrofit tank, I am just not clear on how the air could "burp" out through the connections that are going to be below the water line, once 8 or so Gallons have been used up. It's a sink full of dishwater and one shower, and then it backs up into the shower pan.

gerbermania · 10-27-2003, 08:25 PM

The grey tank needs a vent, just like the black tank.

The grey tank has gases build-up, similar to that of a black tank, and therefore needs to vent. Also, when you drain the grey, the backpressure will siphon out the the p-traps, allowing smells to escape. The tank will drain faster with a vent, because it doesn't have to gurgle or siphon.

According to the 1972 AIRSTREAM service manual, grey tanks have a separate 1-1/4" vent from the black tank. That being said, most people dump one at a time, so it may be possible for you to combine the grey and black vents into a "vent stack", so as not to add another hole through your roof.

I suggest you go to your local hardware store and buy some "spa-flex schedule 40 flexible pipe. It bends really easily, conforms to the curves, and uses standard ABS fittings. Use a standard 1-1/2" slip-fitting, with "eternabond" to seal it against the tank, to connect the new vent to the existing grey tank. Then attach a reducer fitting to go from the 1-1/2" slip to 1-1/4" pipe. Snake the spa-flex over to the black-tank's vent pipe, and cut it into that pipe by adding a wye fitting.

Be sure not to allow the vent to run perfectly horizontal... it needs to allow positive drainage back to the tank, this is for both sewer gases and moisture.

In case someone suggests it, do not just use an Air Admittance Valve to vent the grey tank. Though they are easy to put in and will help the tank drain properly, it won't allow gases to escape... they will just build-up.

christopher

uwe · 10-27-2003, 08:56 PM

Christopher,
Thanks for the advice. I found a vent stack that goes up the rear curb side of my trailer. It connects to the drain pipe from the sink, and it goes out the top opposite of the black tank vent. I was thinking of running the vent hose to above the drain entry to that vent, from the highest point of the grey tank.
Thanks again for your post.

markdoane · 10-27-2003, 09:00 PM

Yeah-vents are good. In addition to relieving air, they also help aerobic bacteria keep the tanks smelling good (well, not good, but better than the alternative anaerobic smell). I haven't installed my retrofit grey tank yet, but it does have vents on opposite sides. This is so if I park off level, I know at least one vent will be above the water level. If your tank is long and mounted across the centerline you may want to consider two vents. I plan to run them up opposite sides and converge at a single roof vent.
Also, mount a tee on one of the vents with the vent on the side leg and a threaded cap on the open end. You can use this as an inspection and dipstick port.

**Chuck** · 10-28-2003, 08:18 AM

Uwe, do you see why I was confused now, in our previous discussion on this issue?

That tank certainly looks to be bigger than 10g, and I couldn't for the life of me figure out how it was venting.

59toaster · 10-28-2003, 09:03 AM

Quote:

Originally posted by markdoane
Yeah-vents are good. In addition to relieving air, they also help aerobic bacteria keep the tanks smelling good (well, not good, but better than the alternative anaerobic smell). I haven't installed my retrofit grey tank yet, but it does have vents on opposite sides. This is so if I park off level, I know at least one vent will be above the water level. If your tank is long and mounted across the centerline you may want to consider two vents. I plan to run them up opposite sides and converge at a single roof vent.
Also, mount a tee on one of the vents with the vent on the side leg and a threaded cap on the open end. You can use this as an inspection and dipstick port.

Mark:

Where did you source a tank to retrofit? any measurments?

I was getting ready to buy some aluminum sheet and make one. I was going to make a tank 4 inches tall, 54 wide and 24 deep. I was going to alow 1 inch to hang below the frame rails and mount right behind the axle to keep the weight forward and keep it from being dragged.

uwe · 10-28-2003, 10:17 AM

59toaster,

try www.rvpartsoutlet.com for holding tanks.

They have many stock sizes, and also a custom order program. I bought a few items from them ( replacement water heater, friction sway control, gas lamp socks) , and their shipping and billing is very reliable.
You can also check your local marine outfitters, they often supply custom holding tanks to the boating industry.
Good luck!

markdoane · 10-28-2003, 10:22 AM

Toaster:
Here is a picture of the grey tank I got from Accutank
It's 52.5 long, 24 wide, max depth at outlet is 8", depth at opposite side is 6"
Capacity is 28gal. One 3" outlet, one 1.5 inlet and two 1.5 vents. It's a 23H, they have drawing with my added fittings if you're interested. Cost less than $200.

59toaster · 10-28-2003, 10:22 AM

Quote:

Originally posted by uwe
59toaster,

try www.rvpartsoutlet.com for holding tanks.

They have many stock sizes, and also a custom order program. I bought a few items from them ( replacement water heater, friction sway control, gas lamp socks) , and their shipping and billing is very reliable.
You can also check your local marine outfitters, they often supply custom holding tanks to the boating industry.
Good luck!

I'll take a look. I have noticed they have a lot of items on EBAY when you do a search under RV parts. THought about bidding on water heaters they seem to always have up there.
Thanks.

59toaster · 10-28-2003, 10:26 AM

Quote:

Originally posted by markdoane
Toaster:
Here is a picture of the grey tank I got from Accutank
It's 52.5 long, 24 wide, max depth at outlet is 8", depth at opposite side is 6"
Capacity is 28gal. One 3" outlet, one 1.5 inlet and two 1.5 vents. It's a 23H, they have drawing with my added fittings if you're interested. Cost less than $200.

Wow that's near perfect size!. Little tall is all. I wonder how much truble I would get in removing one stringer so I can get it up flat to the bottom of the floor?

markdoane · 10-28-2003, 10:26 AM

Toaster:
And here's the location. I decided to go just forward of the axle. I put it a half pitch forward of the existing crossmember and welded in "guard plates" over the ends to keep someone from driving a screw into the floor and puncturing the tank. The circular openings are for the vent connections.

59toaster · 10-28-2003, 12:37 PM

Nice work Mark.

I think I can make that tank work on mine. Need to get the tape measure out and see if it will clear the rear spring shackle where that drain is.

I'm pretty sure that one of the vents would come up under the bed and the other would come up under the vanity. If I had three it would be perfect. The vent under the vanity would become the drain for the vainity. The second would become the drain for the Galley The thiird would be the vent routed around to T into the roof vent. I would be able to hide all but about 8 inches. That 8 inches would be behind the toilet so not even noticable.

Now what are you going to do about the drain? Just seperate or are you T'ing into the black water?

I'm kind of liking T'ing into the black water so you can flush the slinky out. Problem is that would be pretty low and a big risk of draging.