Straight up OR on the Rocks!

My rain barrel is ready for me!

A wee bit early this year 

but at least I can quench my thirst

whenever I want!

 but what is this huge coin shaped white disc wedged into the opening?

 Let's get my trusty tongue into this discovery....

 It really seems to be in there for good...

 I thought I saw myself in there...if you cross your eyes...there!

I do know that whatever it is

I likes it "straight up"

because I can lick it

and 

I like it "on the rocks"

because it cools me off

after a good run at the beach!