So for my drains from the sinks and into the waste tanks, I decided not to use 3 inch bulkhead fittings that I had seen done elsewhere.
It seemed kind of pointless to be using standard 1 1/2 pipe on all the drains and then have to go UP in size to a 3 inch pipe.
It would certainly not benefit me in any way.
Plus those bulkhead fittings are really pricey. ( $30 ish )
Instead I chose to use shower drains.
They are pretty much the same thing.
With a 2 inch opening. And they were only $8.00 a piece.
The white top just pops off.
I chose the style with a ribbed rubber inner part instead of the straight glue on style.
I figured that it would allow for some movement and flexibility.
Drilled out with a standard hole saw.
Fit real nice.
I did the same thing on the underside for a drain.
To be able to tighten the big nut, it was necessary to cut a bigger hole in the top of the tank so I could reach in.
I cut it part way with a large hole saw.
Then more with a box cutter.
I made sure NOT to cut all the way around so that it did not fall into the tank.
That made it easier to re- glue it later.
Once it was done, I just siliconed it back together.
There should be no pressure or water weight on the top of the tank, so it should be fine.
Holes were not perfect, but it will all be covered up later.
This is all that is sticking above the floor of an 8.5 inch long pipe.
I am using flexible rubber connectors to connect to the sink drains.
This allows for the entire drain system to move a little.
Which I think is super important in a truck.
I think NOT doing this would be as crazy as putting solid copper pipe instead of pex.
Here is a shot of the rear tank from below.
This time I remembered to double nut all the threaded rods top AND bottom.
I also did a 1.5 in drop towards the drains.