Test Fit

So far, so good. A little work with the Surform tool for some final shaping of the bottom, and it's a perfect fit.



Signs of a Previous Holding Tank

These holes were in the boat when I bought it, so I knew that a tank had been here. It also dictated the tank design and placement.

In this image you can see where I've rounded the edges of the plug to reduce corner stress.

The Finished Plug

The plug was covered with drywall compound, sanded, painted, and waxed. It looked great! Although I was building a holding tank, I wanted to approach the problem as one of building a boat. I was hoping that all of the prep work would allow the plug to simply "fall out" after I split the tank. I even slightly tapered the sides of the tank so the plug would lift out. The other option I explored for removing the plug was using acetone to dissolve the plug. I decided against this approach because of the mess, the chemicals, and because I wanted to adding an internal baffle. It was the right decision.

Note that you must protect the foam with something. Otherwise it will dissolve when it comes in contact with the fiberglass resin.

You've probably noticed that I've indented the top of the tank. This was done to accommodate the fittings. I decided to leave the rest of the tank as tall as possible to maximize volume. You wouldn't want to let the tank get that full, but in an emergency, it beats the alternatives.

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