Plastic cap at bottom of pool popping off

[deenya]

This screwed on cap keeps popping off when I turn the pool on

 

[deenya]

This cap is on the bottom of the filter housing

 

[woodyp]

Looks awful big for a drain plug. Is there water in the filter? Do you have decent pressure at a return?

 

[Lake Placid]

It’s a Hayward SP1022C (white) or SP1022CBLK (black). Same plugs different color. If you overtighten them them they will crack/break. Just snug enough to seal the o-ring.