Testing the Bell Siphon

In this picture you see the 800 gallon fish tank on the left.  The grow bed on the right and the sump tank below.  These tanks are built with 2x4 walls filled with fiberglass insulation.  The bottom and walls are also lined with sheets of 1-1/2" rigid insulation..  I added this more for puncture protection, but the extra insulation should also help keep the system at a constant temperature.

Here I'm  testing the bell siphon and it's water tight connection. At first the length of the drain pipe needed to be adjusted so that the siphon would break, but it's working now.  I used a 1" bulkhead and 1" standpipe with a 2" bell.  The bell has 3 - 3/8" legs cut at the bottom.

Sealing the bulkhead to the EPDM has been a challenge. I'm a little anxious about that, so just to be safe I have decided to drain the grow bed, and cover the connection with silicon before adding the gravel today. I finally had to cut a larger hole in the plywood and set a 3/8" x 6" x 6" piece of plexiglass over the hole.
I decided to use 45 mil EPDM in the grow bed because of my concern for the sharp edges of crushed gravel, but the problem I keep encountering is the 45 mill Firestone EPDM is so soft, and stretchy that it can easily be pulled out of the seal.

I used 10 mil Pond Skin in the other tanks.  This was purchased at Home Depot and is not Firestone.  This 10 mil Pond Skin does not have the same soft and stretchy character.  I have yet to install the overflow from the fish tank, but my preliminary tests lead me to believe I will not encounter these problems with the 10 mil.

If I continue to have problems with the 45 mil EPDM I will glue a patch of 10 mil to the 45 mil or if the test I'm performing now proves workable, I may silicon the plexiglass to the EPDM and make my bulkhead seal directly to the plexiglass.