Septic tank lid seal

I have a septic tank with round concrete lids at grade level resting on a concrete riser. As the concrete is a bit rough and uneven, the lids do not seal very well. Depending upon atmospheric and other conditions the area is a bit malodorous.
How is a seal usually formed for such things? Are there gaskets that are used? A ton of plumber's putty? Something else?
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Hopefully they're fabricated well enough to simply seat well enough on their own. Most installations I've seen also have the tank set deeply enough that the lids are below surface by at least a few inches and so the ground prevents any air leakage.
If you can't cover them w/ ground (cover w/ plastic first to prevent dirt entrance), I'd mix up a really thin paste of cement so it wouldn't have much adhesion power and lay an inch around the lip and the set the lid on it. Most any flexible material could be used in the same manner.
--


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Throw in a galon of bleach - it will stop most of the smell!
(just kidding, BTW)
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Put an appropriately sized bead of mortar mix around the top edge of the tank. Cover it with heavy plastic. Set the lid on carefully. there, now you have a surface that matches your lid, and it will still come off easily.
--
Steve Barker





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A lot of them are out of whack, and will only fit in exactly one position. Clean both surfaces and try rotating it until you get the best fit. Take a crayon and mark it when you get a good fit. Do a couple of full turns to make sure. You can make a lever to help you lift it, and if there's a rebar lifter on the top, hang it from stout rope so you can twist it.
Oh yeah. Wear nose plugs, too.
Steve
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How about a little bit of sand? Remove lid, spread a handful of sand around the top of the rim, replace lid.
-rev

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wrote:

Wouldn't all the sand just fall in before you replaced the lid? (Sand in a tank is supposed to be bad BTW - sewage truck drivers don't like because it can't be vacuumed up)
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Just enough sand to fill in the surface irregularities. As the lid is set in place a little bit might end up falling into the tank but I can't imagine that would hurt anything.
It would take two people to lift the lid and gently set it down rather than sliding it in place - which would dislodge all the sand.
Just a thought.
-rev
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