How much toilet offset from black tank is OK?

[Sparky57]

I am redesigning the bathroom on my 57 Overlander. I have the floor out and have ordered 2 tanks- 21 gallon blk and 38 gallon grey- both for under floor mounting. I like the rear bathroom layout- like the original layout- and for space reasons putting the toilet under the rear window makes most sense.

I'd like to hang the black tank as close to the axles as possible and there is a natural spot for it to go in the frame- this design would mean buying a low profile toilet- probably the Sealand Traveller 500- setting it on a 6" stand and then running 3" abs into the tank. The overall run would be about 16" and would have the right slopes etc...

The design works on paper, my question is will this work in practice? Not sure if RV toilets have the flushing power to operate this way.

Alternate design is to:
-move the toilet forward, but that wastes so much space and I'd still need a bit of offset to skirt the frame, or
-move the tank back to the toilet, which is the next preferred option, but I get nervous about the tank being so far back and rubbing ground when backing up my driveway. I can't imagine I'd tow with it completely full (or even a little full!) so I don't worry about weight distribution too much.

Many thanks!

[arodriguez60]

The amount of flushing force from the toilet wouldn't have the power to overcome that distance in my opinion. I think you would have solids clogging the pipe. I would move the black tank rearward to get a direct path to the tank. Most inlets to the tank are straight down. On my 69 I do have approx a 2 inch offset on a 6 inch high platform that has done me well. But I wouldn't go for much more.

[Jammer]

Any sort of horizontal run will pose problems for an RV toilet.

[Sparky57]

I guess it is the low water volume that makes it a bad idea....

If I move the tank back then my rear end clearance suffers a little. How much clearance is enough? I would drop down 4 inches from the BP, leaving about 12" to the ground. Hmmmm

[arodriguez60]

put a string from the bottom of the bumper to the bottom of the rear tire of the AS. any thing above the string should be relatively safe.

[webspinner]

Don't most black tanks sit above the floor, making a raised platform that the toilet sits on? That's how it was in our '71 Tradewind until we pulled it out and put in a composting toilet.

Ideally, solids need to be able to get to the black tank with no water volume at all. The small amount needed to rinse the toilet bowl is not nearly enough to wash solid waste through any horizontal distance.

Also, sewer pipe slopes in houses are precise, but houses don't move around much. There is no guarantee that your trailer will be exactly level every time. Any slope on the trailer could affect the slope of the sewer pipe.

[arodriguez60]

On my 69 Tradewind the Blacktank is below the floor ,on my 73 Safari the tank is above the floor. I just think it depended on layout or just engineer preference . May it was depending if it was made in Ca or Ohio. Ca models generally had the toilet on the street side and Ohio trailers had them on the curbside. Go figure.

[Sparky57]

Originally Posted by arodriguez60

put a string from the bottom of the bumper to the bottom of the rear tire of the AS. any thing above the string should be relatively safe.

I was just thinking that same thing!

Putting the tank above the floor meant the volume was too small, too much wasted space. I have 3 young daughters so the trailer will be crowded and they make good use of my current tent trailer's black tank, so more volume is needed, and I wanted a hose spray nozzle clean out hookup thingy too.

On demand hot water is in the plan too so I am hoping 40 gal grey is big enough for us all.