I have a water tank that I want to read the level on. I would like whatever device I use to be passive. I have seen the 'cat and mouse'-type weight and pulley device, which doesn't suit my purposes (I would like something self-contained).

The question is: can I take clear tubing, connect it to the outside of the tank at the bottom and run it up the side of the tank to just over the full line? Will I need a vented cap? What about the head pressure on the tube? Is this not advisable for any conceivable reason (assuming the tube is secured properly)?

  • That's how the water level indicators on many electric kettles work. Should work.
    – hookenz
    Sep 13 '17 at 23:46
  • Yes, it needs to be vented. Or the top of the tube should connect back in to the tank. With the vent, you could get leakage from the vent if the tank over-fills. If the filling system is counting on back pressure to regulate the tank level, then you will need to connect the sight tube back to the tank.
    – longneck
    Sep 15 '17 at 13:27
  • @longneck is correct - note also that a sight glass on a pressurized tank will require shutoff valves at both top and bottom. Sep 15 '17 at 16:43

There should be no fundamental problem with this, provided that the indicator tube is not closed at the top. You can either install a vented cap to keep debris out, or connect the top of the tube to the top of the tank.

As a callow youth I assisted in the construction of a water tank indicator like that. I have also operated a steam boiler with similar indicators. If common experience is any guide, your most likely problems will be:

  1. Discoloration of the inside of the tube, from scaling or even from algae, that makes it difficult to read the level.
  2. Hidden blockage that prevents the free flow of water to and from the tube.
  3. Damage or fracture of the indicator tube leading to a serious leak.

Against (1) you should make the tube dismountable so you can clean or replace it. This will require a shutoff valve and a threaded joint or union.

Against (2) you can rely on dismounting the tube and briefly opening the shutoff valve, or you can install a drain valve that you can open briefly, thus restoring your confidence that the flow is unrestricted.

Against (3) you must install a shutoff valve.

Note that the combination of the shutoff valve and a drain valve can also serve to drain the tank when necessary. If your tank presently has a drain valve, this might be a place to install the indicator without boring any more holes in your tank.

Here is a sketch to show the order of the valves and fittings for a couple of possible tank drain positions: DIY sight glass installation The order of the fittings must be: Tank Tap -- Shutoff -- Sight Glass Connection -- Drain Spigot.

You will have to shop for the transparent tube and the compression fitting together. Don't bother with a big-box home supply store, go to a plumbing supply shop and talk to the oldest guy there.


I would call an HVAC company that works on boilers and have them install a "gauge glass" in the tank.They can use standard gauge glass, Pyrex gauge glass or plastic/vinyl tubing or other material depending on temperature and pressure. They would normally install the gauge glass with shut off valves to allow for cleaning and/or replacement of the sight tube, and a check valve in the lower glass to slow the leakage of water in case the tube breaks or becomes loose. Those of us that have serviced or installed boilers are familiar with this procedure. If this is how you proceed, make sure that you purchase at least 1 replacement sight tube and if possible a tube cleaning device.


I have a set of 2500 gallon tanks connected together that catch rain water from a shop roof to be used for watering our greenhouse during the summer. I placed a piece of clear tubing from the bottom of one of the tanks and ran it up the side. at a glance I know how much remains in the tanks at all times.

Your Answer

By clicking “Post Your Answer”, you agree to our terms of service, privacy policy and cookie policy

Not the answer you're looking for? Browse other questions tagged or ask your own question.