What do I have to buy to seal this lav drain?

[september]

Currently the drain in my bathroom is open and not sealed causing minor leaks here and there.

What do I have to buy to seal it correctly? I measured the exterior pipes and one seems to be 1 3/4 and the other 1 1/4.

Picture of what it currently looks like: http://imgur.com/SQKpy86

 

[Terry]

You should be able to use a 1.5" x 1.25" reducing slip joint washer.

These are the p-traps that I use, and what they come with.

 

[Sponsor]

 

[Gary Swart]

First thing to do is get rid of that flex pipe and plumb the drain correctly with the pieces Terry has pictured.
Flex PVC fittings are trouble waiting to happen. They are a good example of things are are sold that should not be.

 

[Dj2]

From the picture, it looks like you will need to get an extension tube for the down side from the sink to the trap, in addition to all the parts mentioned before.