how far back can I put the toilet in my MCI

[NJT5047]

Jon has introduced another possibility.  For a less expensive, but totally functional system, locate a small holding tank (a 'pony' blackwater tank) in the location of the OEM tanks...curb-side engine room attached beneath the floor...similar to the MCI OEM holding tank.   
Install a standard RV pottie that dumps directly into the small engine room black tank.  install an RV outlet macerator on the blackwater 'pony' tank and pump forward into a main black tank.
The 'pony' tank would only need maybe 5 gallons capacity.  That's the size of an outboard  motor portable fuel tank.  You could double the capacity to 10 gallons in order to avoid cycling the macerator pump. 
JR

 
 

[Sean]

There is a third option and that is to use a pressure assist household toilet.  http://www.flushmate.com/
You can get them as low a 1 GPF.

First off, 1 gpf is twice as much as even the air Microphor, which is already too much if you intend to do any boondocking.  We struggle with it.

But, more importantly, ANSI/NFPA 1192 prohibits household style toilets (AKA "water seal") in RVs, for many good reasons.  All of the solutions we've been discussing are safe and approved.  No water-trap model, including the one you linked, is appropriate for RV use.

-Sean
http://ourodyssey.blogspot.com

[Tony LEE]

Leaving the toilet in the original location at the back may well result in a smaller living area than locating it over the tank in the rear bay - and when you add the cost and trouble of having to use alternatives to the simple straight drop toilets - you  may change your mind.  There is a good reason why most of us sit and think for days trying to come up with a good reason for retaining the original position and then rip it out anyway.

Next question is inevitably "help!  How do I get the tank out"

Answer "with great difficulty and a fair bit of missing knuckle skin"

[gmpd4104]

toilet in the rear is generally not a used option as that location means that if you have guest and they need to use the room, they have to walk through your bedroom.

[BG6]

I want to put my toilet as far back as I can. What is the farthest back I can possiblly put my toilet in my 8?

Are you trying to discourage tailgaters . . ? 

You are best off putting the toilet where you can have the blackwater tank directly below it, unless you are planning to use plenty of water in the flush.  Highway coaches put the sandbox all the way at the back, with a relatively small blackwater tank.  For a conversion, you generally will put your black tank in a cargo or tag axle bay, but you can run a pipe slanted down to the tank, and use enough water to move solids all the way to the tank.  If you can't use that much water, solids will clog the pipe.