Black tank drain size

[JonK-ClassB]

I would really appreciate your insights. I'm thinking of adding a permenant mounted macerator pump. My research shows that the pumps on boats typically have a 1-1/2" inlet to the macerator. I'm wondering why I couldn't do the same. I want to carry either the pump, or to just stick with the slinky hose, but not both. Yes, a pump is more likely to fail than the slinky though most users of macerator on this site seem to be problem free.

I'm thinking my plumbing could be simpler if it was all -1/2" and if the pump failed the resulting mess when the pump was removed would be much smaller than if 3" pipe is used. Of course all this depends on our poop being no bigger than boaters'.

I know the industry standard is 3", but is it really necessary? I generally find standards are useful, is it still in this case. I really don't want to make a cap decision.

 

[Johnnyfry]

The Macerator pump on my RoadTrek 210P is a standard SurFlo marine pump with a 1 1/2 inch inlet. There is a reducer to fit the standard 3 inch pipe to the SurFlo input but otherwise it is standard.

 

[rowiebowie]

My macerator inpeller was out when I bought my "b" at 6 yrs. old (prior owner could have abused, I have no way of knowing). Motor would run, but nothing was being pumped. I chose to replace the entire unit instead of takling the messy job of opening it up.

As previously stated, the macerator "twists" on the standard 3" bayonet connection. The old one pictured below had a 2" reducer on the intake end, but the new one did not.

I had good access, so it was as easy as twist it on, bolt it in place, and connect wires to the existing power switch. The small hose is a breeze to handle, no messy connecting/disconnecting, and a cap keeps any residual inside.

 

[Davydd]

Well I can regularly stop up a 3" pipe because I have been accused of being full of S***.

You mentioned boats. They have when below the hull upflush toilets or macerator toilets where a macerator is built into the toilet so they are really sending an already macerated slurry to the black tank which is then pumped out with another macerator to pump out black and grey water. I was considering a macerator toilet but found they use way too much water for a B to handle unless you want to fill frequently. Here is an example...

https://www.saniflostore.com/Saniflo-Sanimarin-48-Marine-RV-Toilet-SN48.htm

 

[rowiebowie]

Not knowing anything but a macerator toilet, is the stat below high consumption? Frankly, when used overnight for #1 only, most of the liquid flushed is provided by the users and much less than the .31 gal is used to rinse the bowl. But as I've mentioned previously, #2 requires a final flush of about a quart to make the bottom water clear.

But again, not knowing anything else, it's hard to imagine where any extra water is used. Certainly that may be different in a home basement or marine application where you need to pump uphill, but an rv setup uses gravity for the most part just like a standard toilet.

 

[Davydd]

I don't know much about macerating toilets either. ARV installed one and tested it and it consumed more water than a gravity toilet and more water than the manufacturer's stated specs. I have a back of the rear axle toilet in my design and they are rethinking a custom black tank for gravity toilets in those situations in their vans. Otherwise I would have to raise the whole bathroom floor to get a 3" drain over the back axle. They have put in composting toilets in those situations as well. I don't know if they have installed any cassette toilets. They are down on composting, cassettes and macerating toilets as they still think the RV gravity toilet to a black tank is best. They have an industry leading, I think, 40 gallon fresh water tank in a Class B and they think I would be disappointed still with a macerating toilet. I'm working with them to resolve my design. It seems placing the toilet behind the back axle opens up more flexibility in the design of 144 WB Sprinters.

 

[GeorgeRad]

Have you considered marine vacuum system - https://marinesan.com/vacuflush/vacuflush-toilets-generators-info/

 

[Davydd]

The Vacuflush seems overly complicated and takes up too much space if I am reading right. I question the 1.5" outlet.

 

[Snowy]

Davydd:

I saw an ARV video in which they used a removable macerator pump after the black tank to pump uphill and farther away. They made a removable design so that if the macerator ever failed, you could just take it off and use gravity to drain the tank.

Are they still installing this system?

 

[rowiebowie]

Davydd:

I saw an ARV video in which they used a removable macerator pump after the black tank to pump uphill and farther away. They made a removable design so that if the macerator ever failed, you could just take it off and use gravity to drain the tank.

Are they still installing this system?

Since ARV's reputation is to build 'em however the owner wants, my guess is they will do it.

That is basically what is on my '2012 Airstream Avenue. A macerator pump that is accessible at the bayonet dump connection. If my macerator were to fail on the road, I could remove the supporting u-bolt and wires, twist it counter-clockwise, and use a 3" slinky hose to dump.

But that would be in emergency situations only, as I'd get a new macerator on there pronto. So nice and easy to dump with one.