In that case I would proceed as follows:

(1) Tag it as waste_disposal, or waste_basket, anyway which would be much more correct than the grill as far as I understand you.

(2) Look for the correct waste tag, which could be this one, see https://wiki.openstreetmap.org/wiki/Tag:waste=ash, or for more options https://taginfo.openstreetmap.org/keys/waste#values

(3) In case no tag would be accurate enough, you could still ask a question ins the OSM forum...

Cheers!