Often used for plumbing tests, these plugs thread into tees and inflate to block flow across the pipe. After your test is complete, deflate the bladder to drain the fluid from your line. Leave the plug installed while the draining the pipe—the threads create a leak-free seal, so no water will splash out. Also known as pneumatic plugs, they can lose pressure over time, so they’re designed for temporary seals. To inflate, use a hand pump (not included) since an air compressor might overinflate and burst them.