Terrible Advice Tuesdays (T.A.Tues): The Worst PVC Pipe You Can Use For Your Saltwater Tank

Terrible Advice Tuesdays (T.A.Tues): Schedule 20 PVC won’t work for plumbing a saltwater tank due to the pressure in the lines.

The rest of the story: For those of you who don’t know, the higher schedule number (20, 40, 80), the greater the wall thickness of the pipe. The argument here is that schedule 20 PVC is so thin walled that it will fail under the demands of a saltwater tank.

Let’s set the record straight on a couple of things to start:

  1. The pressure (psi) inside your drain lines is nearly zero, assuming you aren’t flooding the lines completely. Even if you flood the drain completely, the psi is still really low.
  2. Even though your return lines are pressurized, the pressure in them is still low.
  3. Schedule 20 PVC pipe is rated up to 200 psi which is WAY more than you’ll need for your tank.

Ok, so what about smashing through schedule 20 pipe. It is thinner than schedule 40 right?


That being said, I’ve accidentally hit schedule 20 PVC pipes on saltwater tanks with protein skimmer cups, return pumps, and various tools and never broken through a pipe. And if you are breaking the pipes on your tank, you either have serious anger management issues, or you are trying to do something with the pipe that it wasn’t designed for.

Given those facts, it is really easy to see why the advice that “schedule 20 PVC won’t work on a saltwater tank” is horrible advice.

For the record, I frequently use schedule 20 PVC pipe on my tank builds and I’ve never had a problem with it.

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Comments for this article (19)

  • Mark H. says:

    Mark, I have used sch20 in several applications without any issues, it is becoming harder to find (in my area) these day. People need to realize that the plumbing is not designed to be a jungle gym for the kids…

  • Michael Horton says:

    I like using the schedule 20 for drain lines, since it has a slightly larger inside diameter due to the thinner wall. The only disadvantage I have found is that I find it harder to cut with PVC cutters as it tends to bend in the jaws and will sometimes crack instead of cut. (I use el-Cheapo cutters). I imagine it would actually be easier to cut with a saw than schedule 40 though.

  • John Vandersloot says:

    Why take the risk? As a portion of total build cost the PVC pipes and connectors are at best minimal. I think anyone with 20 currently in their existing build should rest easy based on the information above however if you are in a new tank build who could justify not going to at least 40. 80 is way overkill but it is what I will use because my tank builder suggested it for the bulkheads……which are far stronger. In addition, based on comments above and my own experience the 40 is easier to work with.
    Mark I have your complete set of books and really got the impression you really advocate not skimping when it comes to critical components. A chain is always as strong as it’s weakest link.

  • Aric Doyen says:

    I’ve worked with all of the different type of PVC pipe and I use schedule 80. Not because of pressure but for the peace of mind. Schedule 80 often comes in threaded nipples up to 12″ in length and down to 1″ in length. I had schedule 40 with slip fittings and glue but the joints soon came loose. So I switched to the schedule 80 nipples with schedule 40 threaded fittings. I used a union near my pump so I could easily remove it for maintenance. I haven’t found threaded schedule 40 before but that’s not to say it isn’t out there. I don’t have a pipe threader to thread my own pipe so the schedule 80 was my only option.

  • JasPR says:

    schedule 80 is ridiculous overkill in an aquarium application. Having said that, there is NOTHING prettier than well crafted multiple lines done in schedule 80. And in 2013 the presentation of ‘whats under the hood’ in the marine hobby is immense. Like a chromed engine in a US muscle car or mink seats in a Rolls, the finishing touches grab the Ooos and aaahs. No problem, the hobby should be fun and bragging rights are part of the fun!
    Rule # 1– make your hobby fun. 🙂

  • Jestep says:

    I just wish they would make SCH 20 and 40 in a dark grey or other non-white color. With that being said, I tend to use PVC to hose barb connectors and flexible braided tubing whenever possible. Just makes replacement, initial routing, and maintenance a lot easier.

  • Jestep…you can get sch40 in dark grey. I’ve never seen sch20 in anything other than white though.

  • Steven says:

    I like to break out the heat gun with sch 20 and do my angles with nice gradient sweeps when room allows. In the grand scheme whatever you like right? I love using sch 80 for supply lines but usually it’s plus 1 sch 80 fittings (bulkheads, valves and unions) on sch 20 or 40. My .02$ And 5 bucks will get you coffee from Starbucks

  • Mayja says:

    Voila! Schedule 40 multi-color PVC pipe!!


    You’re welcome 😉

  • Stephen says:

    I have used sch 40 on long runs within my basement sump install and no issues. I use slip and glue when possible; more reliable than ptfe tape and threaded fittings IMO. Instead of barbs and flex you can find spa flex that will glue straight to slip fittings at most big box stores. This works great when flexibility is needed; can also lower the amount of head loss in return lines from multiple 90s.

  • Chad says:

    I also use schedule 80 pipe for peace of mind. When you’re spending thousands of dollars on your setup, why not spend an extra $200-$250 on plumbing. Plus a lot more places have scheduled 40 or schedule 80 then they do schedule 20.

  • Pierre -Yves Bouic says:

    I was a plumber some time back, and even though I live down under there are a few pointers I’d like to suggest. We don’t have the same talk schedule etc. but what we call Aust. standards tells us what to use in different situations, anyway I use pressure pipe ID 25mm, that would be 60 or 80 for all supply lines, and returns, but return lines or drain lines I don’t glue (thread tape instead) because it allows you to pull it all apart to clean. I’d recommend not using primer (PVC cleaner) before you use PVC glue as its carcinogenic and takes years to get out of your water lines, and the pressures are not high enough to need the extra bond the priming gives to a glued joint. Also after cutting try to remove the burr on the outside & inside (gunk builds up on the rough edge) of the cut pipe with a round file or similar. This is because when the pipe is pushed into the fitting a burr will push the PVC glue out of the contact area. Lastly always fit pipe brackets to take the strain away from connections, bulkheads or pumps. Use coated pipe clamps so the salt doesn’t rust bare or galvanised metal areas, or even plastic u-shaped pipe braces are perfect. Lastly painting you pipework is pleasing to the eye, as long as you don’t use the wrong type, ask for non toxic paint. Buy the best shut off valves that are easily turned ( “O” ring lubricated, as a wrist breaker is no fun & can cause leaks when you stress the pipeline).
    Whenever you undertake plumbing without much experience, draw the pipeline before, measure twice, cut once, and if you are stuck ask for help.

  • chip says:

    Pierre -Yves Bouic , it is nice to hear someone that eally knows what he is talking about. I am also a plumber and what Pierre -Yves Bouic said is exactly right. Plumbing is not for novices.

  • Hurting2Ride says:

    Re: “skimping” with schedule 20:

    A typical aquarium pump maxs out <15 ft of head. So let's say you go nuts and get a pump that maxs out at 30 ft of head. 30 ft of head pressure equals 13psi. So that no one thinks that's a typo, yes, 13 psi.

    So let's say you go extra extra crazy and somehow generate 100 ft of head pressure: that's equal to 43 psi. A far cry below the 200psi that schedule 20 can handle.

    A real world note: in-ground pool installations use schedule 40. Think about the force generated by a typical pool pump compared to your aquarium…

    I personally use mostly schedule 40 because 1) I find the additional stiffness easier to work with 2) it's less likely to get crunched when stored in my garage and 3) it's the most common schedule to find especially if you need something in a hurry.

    There may be reasons to use something higher than Sch 20 but operating pressure is not one of them.

  • Pierre…if the PVC primer is carcinogenic how can it be approved for drinking water? I’d think the fact that it is toxic would make it unusable for drinking water

  • Pierre Bouic says:

    Mark to answer your question, as far as I know primer is used on drainage lines for sewer grade PVC and not on water supply lines, as these are either copper or these days for cost reasons flexible plastic with compression fittings, so as far as home plumbing PVC primer is not meant to come into contact with potable water. However because we are essentially using PVC that was originally designed and meant for draining waste water, sewage, in the pipelines for our aquariums so no governing bodies (drainage commission, water boards) are concerned.
    The use of solvents to obtain strong bonds in joining PVC is not needed because it was meant to give better bonds when suffering jolts, stress cracking etc, and can be done without. The last point I’ll make is that primers, solvents contain similar chemicals to acetone & colours to show its been applied when plumbing inspectors check the work as its mandatory for sewage lines, and because its on the outer surface of internal fittings or outer side of pipe it doesn’t need to come into contact with pipelines if care is taken when applying. Hope this helps, love the live Q and A sessions.

  • Bruce Bailey says:

    why take the risk ? John ,WHAT RISK ! the stuff is rated at 200 psi, Ive used 20 for as long as I remember,its been so long that I think I was using it before it was invented! and never ever ever had a problem

  • Majdi El-Ahwal says:

    Hello everyone…first post here, but long time fan of the website and youtube channel. Where can I find schedule 20 pipes?…I’ve tried Home depot, Lowes and Ace Harware.

    Thanks in Advance,

  • MikeyB73 says:

    I use schedule 20 for most of my Hard Plumbing of my reef tank. I did some maintenance on the tank about 3 years after the plumbing was finished and I had an issue with the schedule 20 piping actually cracking when trying to work in the sump. So, I believe the Salt Water can affect schedule 20 more and earlier than the other grades causing it to become more brittle. This is only a problem if you need to move or adjust your plumbing later in the life of the tank. I find the same problem when I use schedule 20 for my sprinkler and it is exposed to sunlight and or elements. I think I am going to move to use more flexible tubing for many of my runs with hose clamps.

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