Drain Plug for Lifetime Wave Kayak

Our kiddie-sized Lifetime Wave kayaks have a drain hole drilled in the bow on the upper deck, and we've lost the plugs.  The kayak hull filled with water after just a couple hours goofing around on the lake.  I'm assuming the open hole on the upper deck allowed the air inside the hull to displace rather than compress as water leaked in from underneath.

Printed in Filamentum Flexfill 98A TPU.  Version 1 is as shown in the photo; version two includes a loop for a retaining string, to reduce the risk of losing the plug when we remove it to drain the hull.
 

I've included the Fusion file if you want to make edits.