Understanding Septic Systems | Ask This Old House

Sir in our backward 3rd world countries where there no central sewage systems something like this system albeit not so sophisticated has been used for centuries.

Is there a step-by-step guide on how to build such a septic system? And above all, how to calculate the size, the dimension of these chambers and the drain at the end?

Yep you're TOILET is not a TRASH CAN 😉

Excellent presentation

Thank you

This was great, thank you!

Great video. Question about the old clay pipes leading to the tank. Is it important to have them lined or replaced before there could be a problem? Thanks!!!

We're new homeowners in CA, with a septic system. Home is 1960.
Please provide a list of products to avoid for sinks, toilets, etc to keep our system running smoothly between pumps.
Thanks

I live in a tiny town, about 12 miles from a city. I have a 1500 gal cement septic tank built back in the 1930’s, for my home. A few years ago, had relatives visit, and they were telling me they needed to dump their RV’s black water, so could I recommend a place to drive to in town? I said why go all the way to town? Just run the hose into my septic tank. I opened the access lid for them and in a few minutes their RV’s black water tank was empty. They asked if they should dump the grey water, too? I looked into my septic and it wasn’t full to the top, so I said sure, why not? So they dumped the grey water in and I closed the access lid up. About a month later, I had flooding from the septic in my yard. ?! I’d never had my septic back up before, even when I’d had several people stay in my home for lengthy visits. I called the septic cleaning company I’d used every few years, they pumped it out, and they recommended this expensive enzyme additive to get it back to running normally. I had to put in about three of those $90 + gallons, and my septic seems to be working okay, now. Something in that RV’s waste water, messed up my house septic tank’s way of ‘processing’ the waste water. We don’t flush paper into our tank, or let grease go down the sink. So to this day I’m not sure what happened, but I learned a very expensive lesson!

coffee grounds don't decompose?

Been watching this old house forever and have learned so much, but you missed the boat a little on this one. A healthy septic system has bacteria as well as enzyms. Enzyms are great for grease, hair, etc in the pipes especialy. But is anerobic bacteria that digests the material when it gets to the tank. You also failed to mention the most important cause of tank problems, namely the overuse of BLEACH in laundry, and DISINFECTING AGENTS used in cleaning products poured down the drain, that kill the benificial BACTERIA. Also would help to advise people on the best time to use enzyms,(pour it down the drain just before bedtime, or better yet before leaving for a weekend, best of all before leaving on vacation) the longer the enzyms are sitting in the pipes before being washed out by use, the better!!! KEEP UP THE GOOD WORK!

This is probably the best basic explanation in a visual form that I've seen on common septic systems. I talked to people with advanced engineering degrees and experience that could never sort out how a septic system works...

He’s guy is an awesome teacher!

I'm more concerned about the septic system your belt is holding back. Just kidding little on-site construction humor

Cutting sentences on a topic. My septic wasn't opened for 40 years when I bought the house still sealed. I pumped it and was told to pump it every 5 years with single person use.

Thank you

Witch side should the sand tee be lower in the inlit or outlit

Wow, out of 1000s of videos, I just needed this one, Thanks a bunch

I miss Bob

Great informative video! I share this with my customers if they have questions about how a septic works.

Basically, septic tank is a filter. The cleaner the water goes out of the tank the longer the fields will last the outlet baffle you want in the sweet spot. It’s wherever the cleanest water is in the tank. Usually around midway. You’re slug which goes to the bottom of the tank and you’re scum layer that goes to the top. Does not do it that fast. It doesn’t like it goes in the tank and separates quickly. It’s not like just under the scum layer it’s clean they’ll be particles going down underneath the scum fort floats back up again, same with the sludge doesn’t drop like a rock, takes time for it to go down, but it definitely separates right in the middle so that’s where your cleaning spot is. Might not be exactly in the middle. That’s why you have to find a sweet spot. Usually an access spot right above the outlet baffle if you check that it should look pretty clean and you know it’s doing good.

Richard sounds like he's dealt with an issue or two with septic tanks.

Laundry detergent.

We have had alot of rain here and there is a black biomat now on the ground. Does it mean its bad or because we had so much rain.

You mentioned this was an “anaerobic” system. I had a lake house where I put in a septic system that was “Aerobic”. Instead of the water leaching out into the ground, it went to a sprinkler system and watered my lawn. Do you have a video of how that system works?

My little 6'5 nephew would clog that entire box at one sitting.

This was an AWESOME explanation. Slow enough to understand but fast enough to not get bored. So what do people do when they have to wash paint and use harmful chemicals?

MMM! Smells like money!

Thank you for sharing the knowledge.

Really good video

I have a really old conventional septic system, but the line between the grease trap to the septic tank is totally clogged. Every time I have the trap pumped out within two to three days it fills up and starts overflowing. The septic company refuses to snake it out, and me being disabled I can't. I heard that if I add lye to the grease trap, it would dissolve the grease in the line. Do you know if that really works??

Holy crap!!! This is amazing! Almost always been on a septic and never wondered how it worked. Thank you

Thank you, this was very helpful and informative. The house I am buying has a septic tank, so now I know.

Here in Maine at least the tank divider is on the top and not on the bottom. This keeps the scum level from ever reaching the outlet and the solids and sink to the bottom of the whole tank. I have never inspected a fiberglass or plastic tank but have inspected 1000’s of concrete tanks. The newer designs are getting rid of the divider and just using tees on the inlet side and tees with floats on the outlet side

So that's how Joe Bidens brain works

nice model demo

Where we are in Texas we can only have anaerobic systems. Can you do a video on an anerobic system, please?

I wish he talked about how bad draining your washer to your septic tank is. I poured about 2 gallons of rubbing alcohol down my drain years ago and it killed the bacteria and backed my tank up.

OMG Richard, you just did more harm than good. Every system should be pumped every 2-3 years. Some states regulate that it WILL be pumped on schedule. THE BIGGEST harm is too much water at one time. If your wife or kids like 20 min showers one after the other, it stirs the sediment up and floats it to the second chamber where it will go to drainfield and plug it up. once it is suspended, it floats down hill. NEVER buy riddex if you have low bacteria, Pour in a small bottle of yeast at night and flush before bed. Riddex or anything else is a scam. The reason septics fail, is the drainfield can no longer absorb water because of silt lining the ground and it all backs up. I pumped and rebuilt for over 10 years, the cause and effect is simple.

Trethewey is an absolute riot!

Understood 🎉

How is it a sealed system when there are two pipes above ground venting? They just pumped out from the vent closest to the house.

That guy sure knows his septic tank and septic tank accessories ah tell you hwat.

If only there was somehow a way to add a pre-filter that could be easily accessible and serviceable. 🤔

🕳️ 💣

Thank you! Very well explained!

I got my septic pumped out last year and the guy almost immediately said "that's what I like to see" and "this is a nice healthy tank." Made me feel good and also made me realize that some people take their job seriously and probably get really annoyed when some tanks are filled with things that aren't supposed to be there.

So the first tank just holds the solids [poop], the second holds the liquids [pee]? And when the second tank fills up it goes down to the T-pipe and at the end of the T-pipe holes is dirt/earth and thats that?