This is the hardest part. Slide the pop-up basin drain into the extension tube. Youâll need to feed the slip joint washers into the tube because the fit will be tight. After you get the first one in, press down until the next one is lined up and get that fed in. Be careful to work it so the two tubes aren't crooked to each other. Then get over the thing and pushâ¦agin be careful, before you push, to make sure all the rubber is inside the tube or the hilt will be crooked. I found that if I worked the last little bit of the second gasket on the opposite side of that which I worked the last part of the first gasket, it ensured a straight line up of the two tubes. Also, if you are using the plastic pop-up drain, be careful not to break it. I was able to put a fair amount of pressure on it though.