First thought is that after 18 days unless it is a very high alcohol beer, it is done. Hydrometer wise most beers will finish around 1.1X Was this a kit? Most of them will give expected gravity in the instructions.
With a bucket, if you sanitize the hydrometer well it can be dropped right in. It’s not always easy to read though and you don’t get to taste a sample. A wine thief is a cheap investment.
Here is a good thread about hydrometers Hydrometers You need one, here is how to use one
