After Harvey flood waters broke part of my water system, creating a full on pipe leakage, I needed a homemade fix to substitute for a proper water pipe plug since both the hardware store, and the roads to get there, were flooded!
So if you find yourself in a similar situation here is how you make do and stop the leak until such time as proper repairs can be made.
Step 1: Make an Impromptu Water Plug
As a good plug allows some water to flow past it before it finishes making the seal, thus allowing it to be inserted into a pressurized system. The best thing to use for an impromptu plug, that I found, is a bolt the same size as the nominal pipe size, since the pipe is slightly larger on the ID than that the nominal, which was a 3/4" bolt for 3/4" pipe in this case.
Using electrical tape, or preferably heat shrink, create a stepped seal by first putting one layer of tape/shrink up to the threads of the bolt, and then putting a second layer on over that first layer that stops about a quarter inch from the end of the first layer. You can use additional layers if your bolt is notably smaller than the pipe ID, but I would not recommend putting on layers that go over the head of the bolt as they will be properly reinforced.
Step 2: Prep the Pipe
This step can be done with either a lot of zip ties or a few hose clamps, or a combination of both, like I did. The goal is to setup a hose clamp that you can tighten once you shove the bolt into place, which if you lack a sufficiently large hose clamp or zip ties, can be done by daisy chaining smaller ones together.
Step 3: Insert the Plug
This is the tricky step, with everything lined up insert the plug into the water pipe a little bit, slide the clamp/straps, over the head of the bolt, and then start tightening until the water flow is stopped. All of which is definitely easier said then done.
After everything is in place put an additional clamp/tie around the end of the bolt to prevent the main clamp/tie from slipping off of the bolt.
Step 4: Notes
I originally tried using wine corks to stop the flow though they proved to not be stiff enough for the task, but might be usable if you can temporarily shutoff the flow of water.
Though two layers of heat shrink were used, on a 3/4 bolt in 3/4 PVC pipe you only one layer to make a successful seal.
You don't need a perfect watertight seal, just enough of one to prevent massive water loss thereby allowing the rest of the system to be have proper pressured.