Advice needed on adding waste tanks.

One other thing I would add...since I know you are going to get this advice, and it really may be worth considering...
We have made a couple simple modifications for now and added our porta-potty to the bathroom, while the tank is out and awaiting repair. Thus, there is no rush to repair it. It has been suggested that we just simply go with the porta-potty, as it is simpler to keep up the maintenance on it. The toilet and holding tank combination amounts to being nothing more than a large-scale glorified porta-potty, but it is much more difficult to empty and clean in the stall in the campground outhouse. It just may be worth your time to consider this as an alternative, as I know many folks have removed the toilet and gone strictly with the porta-potty, and mostly just for this reason.
There are a number of factors to consider, when making this choice, for instance the type of camping you may be doing the most. If you are on grounds with facilities available, usage of the on-board facilities can be greatly cut down; if you are in the woods a lot, maybe a larger tank would be more beneficial. But also knnow the availability of dumping stations as well....lots of little details...

I'm out of my league regarding this subject, but you might consider what the capacity of your activities will be for both the grey water and black water tanks and if fairly light, consider one each of the "portable" tanks on wheels that I guess you just slide under the drop lines and quick connect. Small volumes can be rolled to the dump point and the rolling tank returned to service or once emptied put in the bed of the tow truck if you use a truck, and I imagine you will be trucking the Alma.

Update: I'm bouncing all around today and just ran across this post by mobiltec which illustrates what I suggested. Also, I see those rolling tanks on CL all the time, much less expensive once used than purchase price as new. Scroll to the bottom of the first page.

vintagetrailertalk.freeforums.net/thread/4417/sink-drain-vent

Brian,

I have thought the same about the SC, and think I may redo the tank and toilet.

Another thought I have had though, involves the portable tanks. One is necessary with the grey water anyway. So, doing some mental engineering, and think I may rig the pipe from the toilet outlet with a standard bayonet fitting, so it will easily hook directly into the portable tank. The portables have a 3" opening and many new ones are standard-equipped with either the bayonet capability or they have a short hose attached, which connects to a bayonet outlet. They also have a hose-fitting-inlet, which allows for venting and for rinsing with a dedicated garden-hose (many new ones are equipped with a short one of these too). I think I may be able to flush directly with the 3"....and then adapt the grey water down to the garden hose size to run into the other inlet. Thus, one tank for all the outlets, and one trip (every so often) to the dump station.

There is a separate discussion involved too, that some campgrounds will not allow for portable tanks. I have yet to run into this issue, so can't offer much opinion on that matter.

As to the question of mounting the tanks, again, I have limited experience with any of these. The one on the SC, pictured above, was hung and secured below the subfloor, within inches of the bottom of the shower deck and plywood flooring. The line shows in the photo, of where the tank actually hung below the belly pan of the trailer.... It was mounted against the outer skirt, outside the steel trailer frame. The only other experience I have with tanks was on a fifth-wheel we owned one time. It had two tanks that were plumbed much as I described (regarding their outlets), and they were both mounted tight to the subfloor, and hung with special hangers from the steel framework, but not below the outriggers...actually between them I think. Been a while. The best mounting solution may be to mount as tightly to the floor as possible, cut holes through the floor and then thread drain pipes and vents in through the top of the tank.