Introduction: Backyard Dunk Tank

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About: I retired from the USAF in 2005 and now work for a local government as a project manager. I live in a fantastic neighborhood that enjoys getting together to celebrate whatever event happens to be on the cale…

OK, so you’re trying to plan some fun summer activities with friends and family and what is one thing that is always a bit hit at outdoor parties and cookouts? A dunk tank!! The problem is that there is never one around when you need it, and if it is around then you have to haul it in place, fill it with hundreds of gallons of water, then get dunked in water that is full of who knows what after a while.

Well, I have a solution for you. It is portable, lightweight, sanitary, fun for all ages and uses 3-4 gallons of clean water per shot. All you need is a hose and a place to put it.

There are other styles of these tanks around that require power (which may pose a danger around a water feature) or components which are prone to failure, but this design is, basically….wait for it…..a giant toilet!! It uses the same components found in your home toilet of a flapper valve and a float valve, that’s it! Let get this thing made!

By the way, this looks like a complicated build but it goes together very easy, I just try to be very detailed (read verbose) when I lay out the steps.

Step 1: Tools and Materials

Tools are pretty basic:

  • Chop saw or hack saw to cut PVC pipe
  • Drill with bits
  • Basic hand tools

Material – most of the items can be picked up at your local hardware store but I did include some online sources for some of the components:

Step 2: The Flapper

The first step is to make the mount for the flapper valve. There are a couple of different ways to make the mount. I was fortunate to have access to a 3D printer for this piece, but if I didn’t, I would have taken a piece of 1/8” thick aluminum stock bent into a U-channel and drilled to accept the cross rod. The bottom of the mount needs to be pretty flat to facilitate mounting it to the bucket. Fortunately, though, my son had a drafting class at school and offered to draw and print the mount for me. It is 1/8” thick, 1” wide and 2” tall. The holes are ¼” (same size as the fiberglass rod) and drilled 3/4” from the bottom. The larger third side was glued on later to restrict the movement of the flapper so it wouldn’t open too far.

Next, cut the fiberglass rod so it extends past the sides of the mount around 1”on each side. A note on cutting fiberglass; I found it helpful to wrap the cut area with masking tape before the cut and apply super glue to the ends immediately after cutting to prevent fraying. You may also want to wear a mask or keep the rod wet when cutting to reduce the possibility of inhaling fiberglass dust.

Insert the rod into the drilled holes and secure in place with the silicone sealant. Make sure the flapper can fit on the rod and operate freely. You might need to trim the corners of the flapper to allow free opening and closing of the valve.

Now you can drill a hole in the bottom center of the bucket that is slightly larger than the flapper seat ring hole and then attach the seat using silicone sealant. This part is optional if you don’t have the seat ring but highly recommended to get a good seal from the flapper valve. Once the silicone has cured, install the flapper on the mount and line it up over the drain hole. Use more silicone sealant to secure the mount and let it all sit until the silicone is fully cured. Remove the chain that comes with the flapper.

Step 3: The Float Valve

The products I mentioned in the material section for the float valve fit very well inside a 5 gallon bucket but you can certainly use and adapt whatever you may have around from a plumbing repair or what have you. My main concern was to have the refill take less than one minute to keep the dunking activities moving along and this valve is rated for 12.5 GPM @ 60 psi, which, at typical household pressure, is about 6 GPM. It puts about 4 gallons in the bucket in less than 45 seconds.

Locate an area about 1-1/2” below the top of the 5 gallon bucket to mount the valve. In my case this was right at a ridge in the bucket so a little trimming was in order to make the area flat enough to drill out the 7/8” hole needed for the valve. Connect the 3” rod and float ball to the valve and mount through the hole with the valve nut. The final connection is the double female hose connector so you can hook up the garden hose when ready. Test the ball float for free movement in the bucket, sometimes you may have to rotate it to the side a little.

Step 4: The Frame

The frame is basically a large rectangular box with a couple

of extra beams across the top to support the bucket.

We’ll start with a cut list for the 2” PVC pipe:

  • 4 ea - 60” pieces, basically cut 2 of the 10’ lengths in half
  • 7 ea – 30” pieces
  • 2 ea – 13-1/2” pieces
  • 4 ea – 10” pieces
  • 2 ea – 6” pieces
  • 2 ea – 1-1/2” pieces
  • 1 piece the height of your bucket + 4”

First make the bottom frame by gluing 4 of the 30” pieces into a square using 4 of the 90 degree elbows with side outlets (I will call these pieces corner elbows) making sure everything is square and level.

Next glue two corner elbows to each end of another 30” piece, again, making sure the corner elbows are square to each other.

Attach the 13-1/2” pieces to the legs of a tee then the last two corner elbows to the end of that assembly so the regular tee will be standing up when assembled, square and level.

Now glue two of the regular tees to each end of the last two 30” pieces (call these center struts), you know…square and level.

Connect the center struts together with the two 6” pieces then glue the 10” pieces to the last leg of the tees.

The final step of the top assembly it to connect the 30” pieces with corner elbows to the outside of the 10” pieces making sure it is all square and level. I know I am repeating this but it is very important that everything lines up since not all of the pipes in the frame will be glued and you want as little stress on the joints as possible.

Now you just need to put a 60” piece in each of the bottom corner elbows and put the top assembly on the top of the 60” pieces. I did not glue the 60” pieces on either end so I could disassemble the frame for storage but I did secure the pieces into the corner elbows with self tapping screws.

I cut down a scrap piece of plywood the length and width of the center strut section to add strength and stability when the weight of the bucket is added. Drill a 2” hole in the direct center of the board then use screws to attach it to the top of the frame.

Step 5: The Trigger

Now the build gets a little trickier and attention must be paid to sequence of gluing the pieces together to ensure proper operation. Most measurements will not be given because much of the alignment depends on the size of the bucket you are using.

First take the 2” cross tee and glue the 1-1/2” pieces of 2” pipe into opposite ends of the tee. Clean any extra glue immediately since this area must remain clean and smooth.

Measure across the width of the cross tee and the inside lip of the 1-1/2” coupling and 45 degree elbow. Add these up and cut a piece of 1-1/2” to this length +1/4”. Glue this piece to the 45 degree elbow and slide it through the cross tee and 2” pieces you previously glued. The 1-1/2” piece should fit inside the 2” pipe pieces with a little room to spare. Now glue the 1-1/2” coupling to the other end of the pipe you slipped through. This will form a nice hinge that will not slip out of the cross tee.

Place the 5 gallon bucket on the plywood board so the flapper valve is right over the hole in the plywood. I installed a couple of screws on the outside of the bucket to keep it from sliding around. Take the “bucket high” piece of 2” pipe and glue it into the vertical tee on the top assembly then glue the cross tee hinge on the top of it so the 1-1/2” coupling is facing the hole in the bucket. Cut a piece of 1-1/2” PVC approximately 42” long, or as long as you want it for the target arm. Glue this into the 45 degree elbow so it hangs down on the side of the top assembly.

Trigger edit August 2017

Measure from the inner lip of the coupling to the hole in the bucket and cut a piece of 1-1/2” PVC to this length and glue it to the coupling, then glue the 90 degree elbow to the end making sure it is facing to the rear. Next cut a piece of 1-1/2” PVC approximately 10” and glue it to the 90 degree elbow facing to the rear.

Step 6: Putting It All Together

Cut a 10” diameter circle from some plywood for the target and attach it to the bottom end of the 45 degree pipe. My initial attempt was to use 2 screws but that proved inadequate so I would recommend two 1-1/2” pipe clamps bolted to the wood.

Trigger edit August 2017

Install screw eyes to the bottom of the rear facing PVC and the top back of the bucket. Tie off a piece of string or heavy fishing line to the flapper and route it through the eye on the bucket and connect it to the eye on the PVC.

At this point I put a piece of surgical rubber tubing to relieve stress by tying it off to the eye on the PVC and a second eye on the frame. This will keep the arm from going to far in the event of a hard hit which would pull the flapper from it's mount. Make sure the flapper opens when the target is moved to the rear.

Two other modifications I made were to put a ratchet strap over the top of the bucket for safety and hook a few fishing bobbers to the line right above the flapper. The force of the water exiting the flapper was causing it to close too soon so the bobbers help keep it open until the bucket is empty.

Step 7: Getting Wet!!

Time to put the tank in a level place, find a chair to put under it and connect the hose. Here is where my evil side creeps out, though, as I prefer to connect the hose to my lawn irrigation well so the water is a nice 55 degrees rather than the 65-70 degree tap water. Believe me when I tell you, the first shot from this will take your breath away!! Saves on the water bill also.

I use 1lb beanbags I made for playing cornhole as the projectiles. They seem to have the perfect weight to trigger the tank and are light enough so the small kids can participate with no problems.

Thanks for suffering through this intolerably long Instructable, I hope you decide to make this project and enjoy hours of cool fun with friends and family!

As always, please contact me with any questions and feedback is welcome.