Missing Septic Tank Cover

I just had my Septic tank pumped out. And discovered that the prior owner of the house had lost or broken the inspection hole cover. This is not the primary opening, just one over the outflow pipe to the septic pit.
He placed several two inch thick foam squares over the opening, and then placed a metal ammo box over the foam, and pieces of broken cinderblock around the area, and then buried it all. What a great cover!
I would like to create some sort of replacement cover for this opening, since I can't seem to find any for sale. My thought is to try to create a concrete form, but I have never worked with concerte in this way.
I haven't measured the opening, but it is approximately a 1x2 opening. Could someone please provide me with some tips? Can I make a casting or form or something and bury it before it has completely cured?
I hear we are expecting rain the day after tomorrow, so I need to get this buried before my empty tank fills up again!
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Claude Fountain wrote:

If this is a flat opening (no tank I have had has such an opening other than the tank itself so I'm wingng it), just make a form of 2x4 w/ a plywood or 1x bottom a little larger than the opening and pour a slab. If you're concerned about the opening and the rain, I'd just form it in place and lay some plastic over it until the rain is over, then pick it up to strip the form and put it back permanently....
A 80-lb of quickrete is 0.6 cu-ft iirc and a 1.5' x 2.5' x 3" volume is right at 1 cu-ft so 2 bags would be about right. You could, of course, make two of half-width for less weight each if you chose.
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Claude Fountain wrote:

Make a form the size you need, use a small piece of welded wire mesh for reinforcement, put diesel on the forms as a release agent and put a rebar handle embedded in the concrete for a lifting aid.
You can bury it immediately if you put that ammo box back over it. It should be good to go after 24 hours, anyway.
If your tank is completely empty, you should IMMEDIATELY fill it with water or you may get to see your tank float out of the ground.
--
Robert Allison
Rimshot, Inc.
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Claude Fountain wrote:> I hear we are expecting rain the day after tomorrow, so I need to get this

Andy writes: You WANT your tank to be filled with water as soon as you can. If there is a rain, the water table around an empty tank will force it up, and it becomes a big cement boat, and will probably crack in the process. Usually, a pumper will run a hose into the tank and at least partially fill it with clean water before he/she leaves.
Regarding an inspection cover. It ain't rocket surgery..... just dig a hole in the dirt about 3-4 inches deep the same size as the opening and put about one sack of sackrete in it. Let it alone for a couple days..... You should make a lip on it so that it will not fall thru. You can figure this out by thinking about it for a while.....maybe putting a piece of rebar in it to act as a stop.
Nothing wrong with just making a square piece a few inches thick and laying it over the hole.... You are going to put 6-12 inches of dirt on top of it anyway.... Remember, the method the previous owner used worked just fine for many years..... so it ain't that critical...
Andy in Eureka, Texas
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As horrifying as it may have been to see this make shift cover, the foam cover idea may not be so bad because there is a positive seal a loose concrete cover won't have. You could take some heavy plastic wrap and stretch it over the hole and secure with duct tape. Then, form the dirt round the area to make a mold to pour a little quickcrete. If the hole seems too big, or you are afraid the concrete might grip and lock onto the opening, making an irremovable top, take a can of spray insulation foam (the yellow kind that expands dramatically), and fill in the mold with that. When the foam is solid, take it off, peal off the plastic, shape it with a knife to improve the desired shape. Then put inside a simple wooden perimeter form with the cap side buried face down into the dirt. Pour the quickcrete over the back of the foam to a thickness that won't easily crack. Etch a happy face or the name of the coverplate into the concrete for decoration. After the concrete has dried, clean dirt off cap side of foam, put into place, and bury again if you like.
Claude Fountain wrote:

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