Easy-Peasy PVC Water Gun




About: I got an old sewing machine when I was just a kid, and I've been hooked on making stuff ever since. My name is Sam and I'm a community manager here at Instructables.

There are a handful of do-it-yourself PVC water guns on the internet.

This water gun is similar to other versions out there, including this one I shared a few years ago, but with a handful of new tricks to simplify the design and make it easier for people to duplicate.

If you make a few, let me know how it goes in the comments.

Thanks for taking a look!

Step 1: How It Works

This type of water gun is basically a large syringe. There are two main parts: the outer piece which is the barrel, and the inner piece which is the plunger, or piston.

On one end of the piston there is generally some type of seal, that acts as a round, watertight squeegie. This seal allows the piston to draw water into the barrel as you withdraw the piston from the barrel, and to force water out as you push it in.

The hardest part with this style of homemade water gun is the seal. If it's either too tight or too loose, the gun won't work. There are a lot of complicated ways to make an effective seal, but I believe I found a simpler way to get the same results, quickly and easily. I'll explain as we go.

Step 2: Materials

First off, I recommend making six water guns at once. This maximizes the use of materials and should only cost around $30 total. Plus, six water guns seems to be the right number needed to start a decent neighborhood water fight.

Here's what is used to make one water gun:

  • 20" of each: 1" and 1 1/4" PVC pipe (usually available in 10-foot sections, hence the suggestion to make six water guns at once)
  • End cap for each diameter of pipe
  • One 3/4" plug (generally for use on 3/4" pipe)
  • Two o-rings with inside diameter 28mm, outside diameter 34mm, width 3mm. I found these in the hardware bins at an Ace hardware. If you can't find this size, you may be able to use whatever close size of o-ring you can find, using the adjusting method I will cover ahead.

Aside from the o-rings, I bought all my supplies at a Home Depot store.

The only problem I foresee with this water gun design is that the style of the crucial PVC piece--the 3/4" plug--varies depending on the store and who their current supplier of PVC fittings is. That may be a speed bump for some, as well as being able to find the correct o-ring size.

Now, the real secret to this design is dental floss. Yes, the humble, single-use tooth thread that sits undisturbed in your medicine cabinet. You might as well just move it to the workshop where it will see a little more use. It's actually quite handy stuff.

Step 3: Cut Pipe

Begin by cutting 20" sections of pipe. The simplest way to do this is to use a power miter saw. But there are plenty of other ways if needed.

To speed up the process, slip the 1" pipe into the 1 1/4" pipe before cutting.

Step 4: Assemble Barrel

Drill a 3/16" hole into the center of the 1 1/4" cap, and use PVC cement to glue this to an end of the 1 1/4" pipe. Follow the directions on the cement bottle.

Tip: I sanded off the raised logo on the cap to give me a flat surface to start the drill bit when drilling the hole, and used a drill press to make sure the hole was as straight as possible.

Step 5: Assemble Piston

The 3/4" plug is not normally used with 1" pipe, so it won't fit as is.

To make it fit, I used a sanding drum on my rotary tool to sand down an inch or so of the inside of the 1" pipe, until the plug could be inserted and withdrawn without too much trouble.

Place two o-rings onto the plug and mark their height with a pencil.

Glue the plug into one end of the 1" pipe with cement, just up to the line. You do not want the o-rings to be pinched tightly between the flared end of the plug and the pipe, so a little wiggle room is desirable (1/32" extra or so is fine).

Glue the 1" cap onto the other end of the 1" pipe, which becomes the handle. Other fittings could be use if desired, such as a T or elbow.

Step 6: Adjustable Pressure O-rings

And now for the main trick!

Wrap about 30 feet of dental floss tightly and evenly into the gap between the end of the plug and the end of the pipe on the piston. Leave a loose "tail" of a few inches.

Place the o-rings over the dental floss, and check the fit of your nearly completed seal into the open end of the barrel. It should just barely fit with a little pressure. If it is too tight, simply pull a few inches of the dental floss at a time out from beneath the o-rings, and test until you get the right fit in the barrel. You don't even need to remove the o-rings unless you need to add more floss. When the seal is working properly, trim off the loose floss and you're done.

There is a little bit of trial and error required here, but after the 2nd or 3rd water gun for me I had a pretty good feel for what amount of pressure the seal needed to have to function properly.

I recommend doing this step outside next to a full bucket of water, in conjunction with the next step.

Step 7: A Little Bit of Lubricant

Spread a little bit of petroleum jelly onto the o-rings, as well as to the inside edge of the barrel end.

You only need a little; too much will actually be less effective.

Step 8: Have a Water Fight!

After a little testing and adjusting the o-ring seals, you should have a pile of awesome homemade water guns for you next big water fight!

Let me know if you make some. Thanks again for looking!

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55 Discussions


10 months ago on Step 8

I think this might work well to bail water out of the bottom of a boat.


2 years ago

did you get this design from a Popular Science magazine? just wondering, 'cuz the design looks similar

2 replies

Reply 2 years ago

No, but similar piston-type pvc water guns have been around for years.

As far as I know, the o-ring plus dental floss idea is all mine.

Check the publication dates, Pop Sci very well could have gotten some ideas from me! ;)

Shimon - Stan

2 years ago

Great design!

If you make the outer 1 1/4" pipe half an inch or an inch shorter than the inner 1" pipe, you can assure that no one will get pinched.


4 years ago on Introduction

Great job! I've tried to make these before, they're great on raft trips, and always had trouble with the seal. Might I suggest that you make the plunger a couple of inches longer than the barrel to eliminate the pinch factor where the end cap of the plunger meets the barrel.

5 replies

Reply 3 years ago on Introduction

I bet a good compromise would be to put a buffer/stopper on the smaller pipe of some sort. Not sure exactly what would fit, should be spongy and durable though..


Reply 4 years ago on Introduction

Thanks! Good point on the pinch factor. I actually considered that, but opted to simplify things in order to get the most out of my material using the dimensions stated. This way there is virtually no waste, although we do risk a few pinched fingers.

Perhaps a more pressing issue is that they don't float. I didn't do it, but there's got to be an easy way to modify a pool noodle to slip over the barrel, for folks like yourself that would use these on boats.


Reply 4 years ago on Introduction

I hadn't thought of that. But it's an excellent idea! Thanks, pattiemelt!

Maybe if someone gives it a try they can post a comment and share their results.


3 years ago on Introduction

I'm in the middle of making 6 of these according to these awesome instructions. Only difference with mine are the plugs have a hexagon shape instead of round on the outer edge. Still works fine as the rubber O-rings extend past the diameter of it. Had to buy some extra floss, that's the last part. I drilled a 5/16 hole as that was the one plastic drillbit I had in my tool box. I haven't tried with smaller, but the bigger hole tends to "spray" but still accurate (reminds me of the spreader gun in Contra and Super C). We're going to paint these, 3 red and 3 blue (teams) and while it's still hot out have some fun skirmishes with the kids. ;) Thanks for the instructions, this is a really fun project!


3 years ago on Introduction

Not having any luck with mine.. I got the 1-1/8" I.D (1-3/8" O.D) x 1/8" O Rings but they get stuck in the tube when I pull it back out.. That's without any floss or tape so not sure that's the reason..

Thoughts? Thanks

1 reply

Reply 3 years ago on Introduction

Hmm. Sounds like the o-rings are either too big, or you need some lube. (Getting slightly smaller rings allows you to stretch them to fit as needed . . . too big of rings and there's no real way to make them work.)

Just a couple thoughts, good luck!


3 years ago on Introduction

Just made one. I was able to get everything at a box store. I bought the O-rings at Home Depot. PartsmasterPro #218 O rings.

I used plumber grease, or silicone grease. This is a better alternative to Vaseline.

I used teflon tape instead of dental floss. This works better. For one thing, it's easier and faster to apply. Also, because it's 1/2 wide, you can use it to widen the flange on the 3/4" plug at the same time. I had trouble with dental floss because the O-rings would just slip off when I pulled back on the piston. I started with 20 wraps and then added ten more at a time until I had the correct fit.