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Installing a New Toilet Water Inlet Tube

How do I install a new intake line to my toilet?  What are my options to make the connection.

(If you haven't yet, click HERE to open the separate toilet graphics page.  You may need to refer to it.)

There are a number of circumstances where you may need to replace your toilet water inlet tube... replacing the toilet, replacing the flush inlet valve and replacing the tank-to-bowl seal are three examples.  OR JUST IF IT BEGINS TO LEAK AND TIGHTENING THE NUT DOESN'T WORK!

Types of Toilet Inlet Tubes 

The most common inlet tube at the time of this writing (and in my opinion the best looking)  is the chromed copper tube with flanged end and washer,(below left), so I'll use it as my installation example. A brief discussion of it's synthetic cousin, the polybutylene (plastic) tube,  and the braided stainless steel hose follow.

  • Estimate the length of inlet tube you need by measuring between shutoff and the inlet valve. Buy one that is the next size up from your longest estimate! I would also suggest buying a spare tube (which you can return), just in case you... shall we say... goof up! Use a tubing cutter (graphic below right) to trim the tube, not a hacksaw.  Allow a little extra length for the "raw" end that goes about 3/8" into the water shutoff.

  • After cutting, slide all the fittings onto the inlet tube, in the following order:
    1. Inlet valve coupling nut attached the tube to the toilet flush valve... can be metal or plastic.  Slide onto the tube large opening first.
    2. Compression nut (small opening first) attaches the "raw" end of the tube to the toilet water shutoff.
    3. Compression ring (also known as a ferrule) is squeezed onto the tube when the compression nut is tightened to seal tightly against the shutoff to prevent leaks.
  • Insert the tubing into the shutoff valve first, bending the tube slightly in the middle if necessary. Do not make any bends too close to the shutoff end of the tubing. And do not kink the tubing by severe bending!! It is important that the tubing extends at least 1/4" into of the shutoff, or fitting may leak.
  • Move the compression washer so it engages the shutoff and screw on the compression nut a few turns. A little plumbers grease on the threads couldn't hurt!
  • Position the flanged end (with washer in place) under the inlet valve. You may have to bend the tubing slightly for alignment. This is when you find out if you made a good measurement!! Be sure the tubing continues to extend 1/4" or more into the shutoff end as you check the fit on the inlet valve end!
  • If the tube is too long, trim it and try again. If it's too short, pull out that spare you bought. Even the pros always have a spare handy, 'cause we ain't poifect neither!
  • Put a little plumbers grease on the coupling nut threads, and screw it onto the inlet valve, taking care not to start it crooked (also known as cross-threading). Tighten it down securely.
  • Now you can finish tightening down the compression nut. Screw it on hand tight, and then turn it on another couple of turns until it's very snug.
  • Turn on the water slowly and check for leaks. If OK, turn on fully. If there are no leaks within 5 or 10 minutes, you are probably home free!

You can use plain old 3/8" copper tubing if you are especially cheap or don't care what the connection looks like. Look at the upper frame graphics. A special conical washer is used for a compression seal between the coupling nut and the inlet valve. Connections at the shutoff are the same.

Galvanized pipe is so uncommon, except in really ancient installations, as to warrant little comment. It is solid and unbending. If you need to replace it, do so with one of the other styles mentioned here, for future flexibility and ease of repair. Because the pipe is 1/2" rather than the standard 3/8" used in all the other connections, you will need to either get an adaptor to reduce the shutoff valve outlet to 3/8" compression, or replace the shutoff.

Polybutylene Plastic Toilet Inlet Tubing...

Another type of inlet tubing is the polybutylene (plastic) tube.


The wide or conical end attaches to the bottom of the inlet valve using the standard inlet valve coupling nut. These tubes are super easy to install, and can be cut with scissors, a sharp knife, or a standard tubing cutter.

Some plumbers are hesitant to install the plastic lines because they feel that they may fail in very high pressure or temperature situations. If your water is supplied from your own well, you should be able to use these with no problem. However, if you have water pressure over 90 pounds, or if your hot water temperature is over 160 degrees F, you should use one of the other options above, or a braided stainless steel supply tube.

There are only minor differences between the plastic tube and the copper tube installations, except for the fact that the plastic is more forgiving and flexible.

  • These tubes use plastic compression rings to be used with a standard 3/8" brass compression nut. Do not use a brass compression ring with a plastic tube! If the tube didn't come with a plastic ring, get one!!
  • It is critical that the tube extend deeply into the shutoff. The greater flexibility of the plastic works against you if it is cut too short, so try to cut it so it "bottoms out" into the shutoff, or nearly so.
  • As you can see in the graphic, the "head" of the plastic tube in conical, and in a sense is a compression fitting. molding itself against the base of the inlet valve without the need of a washer. A little plumber's grease in the threads of the coupling nut is helpful to make a good joint.
  • Because you are dealing with plastic parts, do not overtighten either end of the plastic tube. It takes less force to make a good seal than with metal-to-metal compression fittings.

Braided Stainless Steel Supply Tube is the easiest of all to install... 

Our final entry into the Inlet Tube Hall of Fame is the braided stainless steel supply tube (below).  It is designed with screw-on connectors on both ends, making a very solid and simple connection at both the shutoff and the inlet valve.

It is extremely flexible and makes installation very easy. Because this type of supply tube cannot be shortened, you must make a fairly precise measurement of the length you need, and then go to the next larger size, just to have some of that old fashioned breathing room.


If you are unsure, buy a few different lengths, and return the unused ones to the store!

If you have too short a distance for the shortest available tube, buy a longer length and bend it into a loop!  OOPS, look like somebody ate the supply tube! Oh well, you get the idea! (P.S. Any snake charmers out there?)

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