Four Holding Tanks?

[drillagent]

Turns out my Montana 3750FL has four holding tanks. The usual fresh water, blank tank, and TWO grey tanks. One for the kitchen and one for the bathroom. I can't find the grey water tank capacities anywhere. The fresh and black are easy to find. But everything I find combines the two greys. Can anyone tell me the capacities of the separate tanks? Thanks.

[Festus2]

Usually, the fresh water tank is not included in the "holding tank" count so in your case, you would actually have 3 holding tanks - one black and two gray.

If you go to Keystone's website (www.keystonerv.com) and look up the year and model for your Montana, you should be able to find out the capacity of the tanks. Sometimes, as you have found out, the 2 gray tank capacities are reported as one; in which case, simply divide that total by 2 to give you the capacity of each separate gray tank.

[WaltBennett]

And, just in case you haven't found it yet - you've also got three valve gate pull handles. The third is usually on the frame around the tires on the street side. Seems few dealers know about this so they don't show you before you take delivery.

[cblong]

if you go to a full hook up site go to the bathroom and pour water a gallon at a time down the shower drain see how many it takes to fill it up. kind of a lengthy process but you would have a definitive answer. then subtract that number from whats listed on the keystone website and you know the capacity of the other one. just an idea if you have the time.

[GaryWT]

You can guess that they are equal and divide by 2 but that is not always the case. As stated above, you might have measure and fill them to be sure.

[JRTJH]

This is just a "SWAG" at the tank volumes, but what the heck....

The totals are listed as:

Fresh Water: 66
Black Water: 50
Gray Water: 93

By some "deduction" and using my own RV as a "model" (I've got a 43 gallon tank) I'd come up with this "logic"...

The Black Tank is 50 gallons and the shower gray tank sits directly behind it.
It probably is a 50 gallon tank. This is because building crossmembers and standoffs is easier when they are the same size and distance apart.

The kitchen gray tank is 43 gallons. I say that because in the RV world, buying in volume means lower prices and Keystone buys 43 gallon tanks for other models. And, because 43 "adds up" with the theory of a 50 gallon shower gray tank.

With this "speculation" the numbers match. I've never seen tanks that were
46.5 gallons. If both gray tanks were the same size, that would be the volume.

But, if knowing the number is "critical" the only way is to pour measured water down the drains (as suggested by cblong) until you find the "full mark" by the shower and the kitchen sink no longer draining. Why do I include the kitchen tank? Who's to say that Keystone didn't change the tanks during the production run? They've been well known for changing up everything else in an RV as it goes down the assembly line.....