managing the dual grey tanks

[TheLexx]

We're looking at either a Momentum 328m or 351m. The decision between the two is whether we want to pay the 3 foot "penalty" to gain the extra bathroom. Since we have triplet 6 yr old boys, we're thinking an extra bathroom would be a good idea.

However the 351 has a lower grey tank capacity at 78 gal vs the 328 having a 104 gal grey capacity. My dealer told me that in both units the grey tanks are actually split into two actual separate tanks. Being that we'd likely use the shower much more than the sinks, I'm thinking that it's much more important to have capacity for the shower. I have a skin condition that requires me to take a 10 min shower daily so I'm going to be the water hog.

Are the two grey tanks connected in any way? IOW do they share capacities? Or are they totally separate? If separate is there a way to connect the two grey tanks so they can share the capacities?

The kicker is the 328 while having only a single toilet, actually has a 104 gal grey instead of the 78 gal for the 351.

[FT4NOW]

A lot of people will get a Valtera twist-on gate valve, place it on the tank discharge pipe and shut it. Then open both grey tank valves and leave black tank shut. This will allow the two grey tanks to equalize, but it will also keep your discharge pipe full of water (not good when it's freezing temps). Make sure when dumping tanks you shut the greys and dump black first, shut black valve when its done, then open the grey one at a time to flush the line and dump the grey tanks.

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[TheLexx]

A lot of people will get a Valtera twist-on gate valve, place it on the tank discharge pipe and shut it. Then open both grey tank valves and leave black tank shut. This will allow the two grey tanks to equalize, but it will also keep your discharge pipe full of water (not good when it's freezing temps). Make sure when dumping tanks you shut the greys and dump black first, shut black valve when its done, then open the grey one at a time to flush the line and dump the grey tanks.

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That makes a lot of sense. Thanks!

[LookingForDirt]

While we still have not received our 2018 397TH yet, I asked the Grand Design Momentum Rep. (Lance I think) if the the two grey tanks were connected internally. He told us they were connected by the drain/dump lines. Basically both tanks converged at a "Y" and had a single dump valve. This would make them self equalizing. I think he is right since there is only one grey dump valve to pull at the dump station. Maybe the Momentums and M-Classes are not the same though.

[TheLexx]

While we still have not received our 2018 397TH yet, I asked the Grand Design Momentum Rep. (Lance I think) if the the two grey tanks were connected internally. He told us they were connected by the drain/dump lines. Basically both tanks converged at a "Y" and had a single dump valve. This would make them self equalizing. I think he is right since there is only one grey dump valve to pull at the dump station. Maybe the Momentums and M-Classes are not the same though.

My dealer told me the tanks are connected so they overflow from one to the other. He never said any thing about a "Y" however. It seems like you hear different things depending on the dealer. Thanks why I'm asking here on the forum.

[Bubblehead]

My 2018 328M has two (2) gray tanks and two (2) gray tank dump valves; one in the forward pass through compartment at the Nautalus station, and one outside behind the left rear wheel next to the Aux fresh water tank dump valve.

[SouthTX]

Sounds like a good idea, but I've never heard of any RV that has on overflow line. Pretty simple to use the Valtera gate valve to let them equalize, though.

[LV Naturist]

You didn't indicate whether or not you will be boondocking often. If you're at a campground with a full hookup, grey water capacity becomes immaterial as you can dump whenever the tank(s) get mostly full. If you are boondocking, you will be limited by the amount of fresh water you have on board anyway, so again, capacity might become immaterial. One hint I'll share... We use biodegradable body wash. When we boondock, we use a hose adaptor cap on the grey water dump, leave the valve open, and let the grey water water the nearby vegetation. By volume, it's more than 99% clear water anyway so it's not like we're contaminating the environment. Galley water is not much different, except for maybe a tiny bit of leftover coffee. We wipe plates and cookware with paper towels over the trash before washing, and don't pour anything down the drain except bio-dishwater and rinse water. Old habits because we often tent camp as well.

John

[Chiefblueman]

We frequently camp in parks that have water and electric hookups but no sewer. This is where gray tank capacity becomes important to us.

[Bubblehead]

To LV Naturist; THUMBS UP! I like your process for gray water use and disposal while boon-docking