I have a brand new septic system and a new 1000 gallon 2 stage cement tank. This is for a cabin that is only used 4 weeks a year with 2 people. Only a toilet is going to the septic.

It will take me a many many years to get the septic tank just full with fluid at this rate.

Should I fill it with water or let it happen naturally over time? I’ve heard that parts of the cement tank not covered with water will deteriorate quicker from the gasses. What is your opinion and why?

2 Answers 2


Yes the system should be filled with water and the installer should have done that. There is a good chance the tanks can float out of the hole if it rains heavy when they are first put in if you do not put water in them. Your second question was valid The average person uses 70 gallons of water per day so if its just you and you only use the house twice a month it will take a very long time for the system to fill up. As for as gases it will be very little do to not much waste entering the system. Also the systems theses days do bot have those issues we precast tanks and have never seen one do this do to gases most break do to a car driving over them or being dropped on installation.


Groundwater/rainwater will fill the tank without even having a toilet connected, assuming it's normally buried and not in a desert environment. The manholes on the top of the tank leak...

I have personally seen a new, empty tank with no fixtures hooked up to it yet fill with water.

I have my doubts about the "gas corrosion thing", since the top of the tank is always exposed to those gasses, and yet the only "tank-top-collapses" I have personally seen or heard of were for steel or wooden top covers on old tanks/cesspits, not modern-style concrete tanks (even fairly old and nasty ones.)

I have heard of concrete tanks losing their baffle integrity, but I suspect that might be steel corrosion related rather than concrete failure (though I don't know that for sure.)

But if your water supply allows and it makes you feel happier, fill it up.

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