Do I really need a black water tank?

[NewbeeMC9]

I'm not sure how high your wheel wells are but you could build a pedestal over it and angle the pipe for better flow.  I'm 6'2' and I wish my potty sat higher.  I have a handicapped toilet in the house and it is great?

good luck and let us know what you come up with.

[Ross]

to be honest I don't even know what one looks like. No doubt they exist on campsites here, but I'm not intending to spend much time on campsites with my bus. Also, the idea of having a black-only tank, and carrying the contents around for weeks doesn't appeal. Although I take the point about the advantage of being able to discretely dump grey-only tanks on the ground, I think I will end up with one combined grey/black tank and dumping properly directly into the sewage system each time.

As long as you have dump facilities convenient to you, this works.  If the dump facilities are at campgrounds and you don't plan on spending much time at campgrounds, then you should plan a system that doesn't require frequent black tank dumping.  Having a full black tank and no place to dump it is no fun...and having to deal with that once a week or more is even worse.  I'd research your dump options before settling on a system.

Ross 

PS...The shower is what fills up the grey tank fast.  If you don't take showers, a combined tank should last a month or more.

[novice]

Jeremy, we have a Prevost with a Liberty conversion.  It has one grey/black tank.  There is however a "grey water bypass".  We haven't used it yet and have not had time to chase it out to see where it goes but if it does what it sounds like, it could be the answer for you.  You could pipe your shower(the biggest user and least offensive) directly overboard or to a hose to run it away from the coach.  This depending upon where you a camping of course.  If you are in a campground, your stay might be shortened greatly if you do.  FWIW

[H3Jim]

Depending on your cooking style, I submit that a kitchen can fill up a grey tank fast too.  I would also like to comment that shower water is part of the stinky part when it sits for a while, soap and body oils and washing your behind.

I have separate tanks, grey and black with an overflow between the two so if one fills, it will overflow to the other. Technically then I just have one black tank, since they are connected.  I am very glad to have the two separate tanks as I boondock a lot.  I can drain out my grey and let the black sit. And by the way Jeremy, that's exactly what a septic system does, the black, it all just sits there and ferments, its what it supposed to do.  I confess I had a few misgivings about pooping in my nice new tanks, and then letting it sit, but sitting is good for it as it breaks it down further, just like a septic tank.  I don't use any chemicals, just have a good 2" vent out the top and never any smells.  Makes it aerobic, as opposed to anaerobic which is really stinky.  Its not really convenient for me to dump my black tank, so I usually go from 3 to 6 months between dumping with occasional use.  I dump the grey on my lot after I get home every time I use it. I have a 58 gal black, and a high end RV toilet that uses only a pint to flush.

My separate tanks and 2" vent is one thing I did right, and if I had it to do over, I would definitely do it the same way again.

[NewbeeMC9]

Whatever you do, make it removable

[NJT5047]

I agree with separate tanks, unless you are certain that you'll never go boondocking...you can lose greywater on the ground....in some places.  You cannot descretely drop combined tanks content.   It's right surprising how much grey water you can create in warm conditions.    
If you and your buds are beer drinkers, double the blackwater tank size....unless you plan to always be hooked to full hookups.  
RV septic tank treatment chems keep odor under control even in the worse conditions.   Some product is environmentally friendly.  
Wait'll some electrical fault (or someone abuses your macerator pottie) results in no macerating of the pottie. That's gonna be interesting!   Macerators are special to repair.
Keep it simple.   JR
BTW, my shower water don't stink!