TANK CAPACITIES ON THE 3900FB

[johncamtravel]

Does anyone know the BLACK tank capacity of the two black tanks on the 3900FB unit. There are two BLACK and two GREY tanks. I think the GREY tanks are 45Gal each?? But I can't find out what the BLACK tanks
are??? The anyone have the answer???

[8.1al]

According to the Montana website the 3900 has a capacity of 93 gallons for grey and black water.

[HOOK]

They are 45 each

[Art-n-Marge]

Well, they're 46.5 gallons each for a total of 93 gallons. Same with the gray sizes too. I have a single black and two grays and they are all 46.5 gallons each. Forget the actual sizes, the sensors are crap so I monitor mine closely. When they read full or you hear burping, or water starts showing at the drains it's time to dump.

[johncamtravel]

Thanks for the replies. Now I know.

[Carl n Susan]

I haven't taken the time to fill the tanks and measure their capacities but in the current models I don't think the tanks are either 45 or 46.3 gal. The website states the black (Waste) tank is 50 gal. and the gray capacity in 93 gals. There are two gray tanks. On most models, one gray is mounted next to the black tank in the "dropped frame" area. The other gray tank is located aft of the dropped frame area. I have poked around the area of the side by side black & gray tanks. They appear to be identical in size with the visible width and depth being equal. Montana states the black tank size is 50 gals. therefore I conclude the adjoining gray is also 50 gals. That means the galley gray tank can only be 43 gals. This does make sense as there is less space in that area.

All of this is speculation. From a manufacturing perspective, it would seem easiest to use one size tank regardless of the application. But the Montana specs show there are at least two, and maybe three, sizes. Perhaps Rich will measure the leaky tank in his rig once it has been replaced. 93 gals. is an unusual number given two tanks. It would be satisfying to know the actual capacities.

quote:Originally posted by Art-n-Marge



...I have a single black and two grays and they are all 46.5 gallons each....

Have you done something to upgrade the tanks? 2006 Montanas came with three 38 gal. tanks. One for each application (black, gray shower, and gray galley).

[8.1al]

The Montana website states 93 gal for waste, 93 for gray. Is this a misprint?

[HOOK]

quote:Originally posted by 8.1al

The Montana website states 93 gal for waste, 93 for gray. Is this a misprint?

The website is accurate. There are two gray and two black on the 3900, each @ forty six and one half. I just use forty five because it's easier to deal with .

[Art-n-Marge]

Thanks Carl... you made me look. My '06 has 38 gallon tanks, one 38 gal for black and and two 38 gallon tanks for gray (76 gallons of gray). If the rig has 93 gallons of the gray or black tanks, and there's two of each tank types, then just divide in half. 45 or 46.5... close enough. We just got back from a 10 day outing and I was dumping all tanks every night or every other night. Our guests and DW love to run the water cuz they can or don't care. And of course the sensors were crap so I'm not even sure they were full anyway, but it's not worth the chance since we had the sewer hookup. Plus the weather was decent every night (cold but not freezing).

[Chip]

Gee, all my waste tanks are Black.

[bncinwv]

quote:Originally posted by Chip

Gee, all my waste tanks are Black.

Bingo