Monument Drain Testing Plugs are durable, quality flexible drain plugs for blocking off drains and pipes. This plug is easy to use and are available in various sizes. Fitted with removable top covers and rubber rings. These plugs are easy to use just place in the pipe end that is being repaired or replaced and simply turn the wing nut knob, this will depress the rubber cone, this will make it expand to seal pipe or tube end with a water tight seal. Monument 1378Z Drain Testing Plug. Size: 100 mm (4 in). Capable of sealing against pressures of up to 1.97 bar / 29 psi.