I am a Five Letter Word

Which 3-letter word can be inserted into all four lines above to form complete words?

P_ _ _ N T

D E _ _ _ S T

S T _ _ _

C _ _ _ E R

What occurs:

Twice in a Week, Once in a Year!

But never in a Day?

Can you name the four days of the week that begin with letter "T"

When you want to use me, you throw me away. 

When you're done using me, you bring me in. 

What am I?

Guess what comes next in the sequence:

1 2 3 4 5 ? 

The answer is not 6. What is the answer?