Fresh Water Tank Drain - At the BOTTOM!

[Waterops1]

I wanted to install a drain in my FW tank that was located at the bottom despite the tank having a concave bottom. I decided to do this by installing a flange on the bottom of the tank and bolting through the tank bottom.

I made a flange out of 3/4" thick polyethylene that measured about 5" on the OD. I drilled eight 5/16" holes that I slipped over 1/4-20 stainless steel hex head cap screws from the inside. In the center, I drilled and tapped for 1/2" FPT.

To get the bolts on the inside, I used the flange as a pattern and drilled up through the bottom of the tank for the bolts. Inside the bolt circle, I used a 2-1/4" holes to put a larger hole. I was able to get the bolts (along with fender washers and neoprene washers) up through the large hole and drop them down into the smaller holes. Fender washers were TIG welded to the bolts to prevent their turning and hopefully help while tightening them up after the flange was in place. To my surprise, I did not need to grasp the end of the bolts with Vise-Grips. All I had to do was tighten up with a 7/16" deep socket.

A neoprene gasket that I had cut was placed over the eight protruding bolt ends and the flange was pushed up over the bolts. I had expected this part to be difficult but it proved easier than I expected. Once all bolts were through the flange, a fender washer, split-lock washer, nut and nylok nut were put on each bolt.

I'll now see if I can get photos posted to show these steps. (Images were oriented when I selected them for uploading. Add me to those that can't get photos uploaded properly