1-1/2" or 3" Diameter Drain Valve for Grey Water Tank

[Gary Hatt - Publisher BCM]

If designing a new waste system, a single would be easier and less costly to install. You lose the overflow feature; other  than that it's a wash.

I, too, like combined tanks, it just seems like a better use of space. But one thing to consider: When combining grey and black water in one tank, after you dump your tanks, you are more than likely to have to flush out your hose with the freshwater supply, which I seldom do. My hoses are in a separate sealed bay, so if they are a bit stinky when I finish dumping them, I am not too concerned. My current tanks are separate, so the grey water flushed out the hose last. However, if either of my tanks fills up, the full one drains into the other tank, so in essence, I end up with mixed tanks.

[Gary Hatt - Publisher BCM]

On the topic of : 
And one more question, would you build your rig to dump both grey and black water out either side of the bus or only on the street side?

I would say that if I could get away with the dump valves on both sides without giving up too much real estate in the opposing bay, I would try to work that.  There have been a few times where that would have been helpful.  So that thought has crossed my mind.  Would need the dump valve and some kind of water flow as well to wash things down on that side.  But as our bus is now, space is very limited and I'd have to through the basement a/c with the sewage.  It doesn't sound promising.   

Kind Regards, Phil

One of the clear advantages of having dump valves on both sides of your bus, street side, and curbside, is the potential time-saving. Imagine driving between two dump stations and being able to dump out of both sides, effectively halving the time it takes to empty your tanks. That's a significant benefit, don't you know?   

[windtrader]

Having dump valves on both sides increases actual convenience the more you spend time on the road and off grid. If you are in parks with hookups all the time, then the issue of tanks is moot. If off grid all the time, then dumping is more frequent to the extent of how much you are on the road. The less trips one makes the actual incidents of inconvenience lessens. So, it all depends, yet again. lol

[luvrbus]

Most grey tanks have a larger capacity than the black ,I was told many years ago by Havery Mitchel the owner of Vogue when I asked why the smaller valve on a larger tank both him and the engineer told me it was because of food sediment settles in the bottom of the tank and the smaller valve draining slower helped break the solids up and mix with the water for cleaning. I am not going into detail about why there are 3 inch valves on a black tank that he told me, I miss old Havery he knew his Prevost, Blue Birds and class A motorhomes

[Gary Hatt - Publisher BCM]

Most grey tanks have a larger capacity that the black ,I was told many years ago by Havery Mitchel the owner of Vogue when I asked why the smaller valve on a larger tank both him and the engineer told me it was because of food sediment settles in the bottom of the tank and the smaller valve draining slower helped break the solids up and mix with the water for cleaning. I am not going into detail about why there are 3 inch valves on a black tank that he told me, I miss old Havery he knew his Prevost, Blue Birds and class A motorhomes

Good to know. I have never heard that.