Drain Plug Leaking Sand

[Teach36]

At the start of the season, we changed our sand in our sand filter. At closing, we always pull the drain plug to drain out the water. However, this year, the sand came out. Now I can't get the plug back on right now.

Can someone explain what I did wrong and what my next steps need to be. Thank you.

 

[Mdragger88]

Is there perhaps a little screen that fell off or is stuck in the cap? Or an oring ? I believe some have a screen type thing stuck in the tube from the inside of the vessel. Perhaps this was dislodged or misplaced when changing the sand.
Some sand escaping is fine - I doubt 300 #’s of sand will escape from the drain hole. When i winterize I leave the cap off & put it in the pump basket for the winter. You may need to rinse the cap & the drain off to be able to screw it back on.
Pics would help