berliner weisse storage question

Primary ferment is done. Now I am switching to 2ndary and dumping in the sick yeast. Going to leave it in the warm water heater closet for 6 mo. Can I just put it in a bucket with a sealed lid, or can I just leave the lid unsealed (no worry about infection at this point right?), or will I need an airlock and bung to release co2?

What is your “sick yeast”? If it is brett I would avoid using a bucket.  Plastic will allow small amounts of oxygen through the pores and that can produce acetic acid (vinegar).

Do you have a link to your original post about this recipe?

I would not use a bucket at all for aging. It allows for oxygen to permeate through the plastic and will stale your beer.

Your best bet is to age in a corny keg.