Bottom of my charcoal grill keeps falling out
Push &amp; twist, very similar mechanism to a bayonet-fitting light bulb.

Three hooks go over three pins, then you turn it to lock.



I cannot tell from the photos whether the pins are in situ.  

Just in case it's not entirely clear from that brief description, you lift the 'bucket' up underneath, it should fit outside the flange on the main structure. Then you slot it over the three pins &amp; twist slightly so it drops into the little locks.