Drain plugs have a tendency to walk off sometimes. Fortunately, replacement drain plugs are available from Bison Coolers. All drain plugs are available in 2-Packs so you can always have a spare.
Bison Drain Plugs (GEN2) are direct replacements for GEN2 HardCoolers only. These have been manufactured since late-2017 and onward. If your drain plugs don't look like these, then you should reference the GEN1 Bison Drain Plugs.