Hi does anybody know where i can find descent sized (20 liters or more) buckets with a tight lid on it in Chiang Mai or anywhere for that matter ?
much like those plastic paint buckets.

I don't want to resort to buying paint or laundry detergent just to get a bucket

Ask a paint shop to buy an empty one - we sell our empty paint bukets back to the shop for 100 Baht.

Try the "20 baht" shops. The open air shops that sell all sorts of stuff. There is one just South of Ghecko bar on the left as you go down.

They sell what are basically food containers with screw on lids but some of them are quite a size, at least 20 litres i'd say.

On the superhiway, before you reach the turn for Arcade bus station.

Approx in the area of Yok, there are a couple of shops selling big blue barrels etc.

One of them is a small open fronted building right on the side of the road.

They usually have 20 lt white plastic pails with lids.

My wife buys hers at Makro.