Aft Holding Tank

I picked out a holding tank yesterday. 

Here it is:

30 Gallon Holding Tank

ECHO has never had a holding tank.  I am building one.

Some considerations.  I hate Wye valves.  I believe the only way to plumb a holding tank is to pump everything into it, and have a suck out port at the top and a drain at the bottom.  I also believe the holding tank should be above the waterline, and as large as possible.

I decided to use the space above the cabinet.  It will be a tight fit, but by custom making my own holding tank, I can maximize the volume of my holding tank.

My rough estimate is it will be a bit under 30 gallons.  While not big, that is a decent size, and I'll met the sanitation laws.  I plan to build a much larger holding tank aft.

I decided to make a female mold. If I had to do it over again, I'd make a male mold and not try to lay the whole thing up at once. 

My female mold worked ok, but it was a challenge.  I've yet to crack the mold, and I'm confident I'll need to add to it on one or both side to make it strong enough to suit my specification.

Here are a few pictures of the mold.

Form plywood cut and stitched (wired) together

 

 Some reinforcing around the middle so I can put pressure on the inside of the form.  I plan to use sand and weights to accomplish that.

  

Maximum strength will come from radius corners--this will allow better drainage. Here I sprayed Great Stuff foam.

 

Next I smoothed the edges of the foam.

 I added some tape to smooth these corners some more.  Later I added some plastic sheeting to cover the entire inside.

I cut and fit two layers of fiberglass mat topped with one layer of cloth.

After wetting it down with epoxy, I folded a layer of plastic on top.  

Next I filled the box with sand and packed it down.  

I felt the wet fiberglass conform to the shape of the mold.  

Finally, I put batteries on top for some added weight.

If I had to do it over again, I'd use a male mold and do the layup in several session to ensure the structure was perfect.   

Since I used a extra slow hardener, I intend to let it set up an extra day.  

Stay tuned!