2019 Momentum 351M Gray Tank Size?

[fool1993]

I have a problem that I can’t seam to get a answer about what size the single gray tank is on the 2019 Momentum 351M. I did find out that there is only 1 gray tank after a lot of calls to Grand Design. According to the Brochure for the 2019 model there is a 78 gallon gray but I was told that was when there was 2 gray tanks and now there is only one and it’s 52 gallon or 39 gallon or so on. The last person at grand Design told me there is only 1 tank and it’s 52 gallon. I’m just not sure if that’s definitely the answer. If anyone knows what the size of the gray tank is please let me know. Thanks for any help.

[fool1993]

Also, does anyone know what the black tank in the 2nd half bathroom size is too? It’s definitely bigger then the front black tank but again I can’t get a definite answer from grand design. The one guy did try to get me a answer and he’s the one that I found out there was only 1 gray tank and that he said it’s 52 gallons. I wish there was a better way then filling up a 5 gallon bucket and see how many the tank holds.

[wingnut22]

I would like to find the answer to these questions as well. We have the same unit. all the specs say it has one 78 gal. gray and one 78 gal black, however there is a separate black tank sewer for the 1/2 bath.

[fool1993]

I did finally find the answer to this question from a great guy at Grand Design. He said I or we anyone that has a 351M has 3 tanks total and all 3 of them are 52 gallons. How it works on paper is you have a front gray 52 gallon and a front black 52 gallon and a rear black/gray because the sink and washer goes into it but they can’t call it a gray because of the waste so it’s called a black tank. So what they do is take that rear black tank and say that 26 gallons is black and 26 gallons is gray so 52 plus 26 is 78 total and that’s how they get there 78 gallons gray and 78 gallons black. Now you really only have a front gray of 52 gallons and that’s for sure. After he said it I was completely dumbfounded because It made so much sense being you use the rear tank for the sink and washer so they can kind of call that gray too. I just couldn’t believe that no one else had that answer. His name was Randy and he is a great guy and Grand Design is a great company. I had a warranty problem and they took care of it and they also don’t mind answering questions. I’m just happy to know that my front gray is 52 gallons for sure or I could say that all 3 tanks are 52 gallons and I hope anyone else that’s wondering now knows what they have if they own a 351M.

[CFDWheeler]

Good to know for sure. I knew I had three tanks, and that the rear was combination grey/black, but did not know each of their capacities. Thanks!