Here's some step by step instructions I think you will find useful.
Lowes and Home Depot will have the pipe and fittings for the best price.
You will need a 2" male adapter, a 2" to 1-1/2" bushing (aka reducer), either an 1-1/2" coupling or better yet, a 1-1/2" flush union, and a small length of 1-1/2" solid core pipe, aka pressure rated.
Go to a pool store for Pool Tite glue, primer, and 3/4" wide Teflon tape. Don't let the glue or primer freeze!
Cut the pipe six inches up from the top of the bushing.
Unthread the pipe from the pump. Go in a place where there is good ventilation and it's warmer than 55 degrees.
Spread some newspaper. Primer and the glue will stain.
Cut a six inch length of pipe if you got the flush union or 7-1/2" if you went with the coupling. Wipe off any loose stuff off the edges.
Prime the male adapter and reducer bushing.
Note that when priming an applying glue, grasp the stem of the applicator. They sometimes separate from the cap otherwise. When gluing, always glue the male end 1st.
Apply glue to the bushing's outside surface and the male adapter and insert the bushing and hold for 30 seconds.
Wipe away the excess with a paper towel.
Prime and glue the pipe to the fittings.
If you bought the union:
Split the union. One half will have an o-ring seated in it. Prime the other end of the pipe and the union end with the o-ring. Wait a couple minutes. Get some air. The fumes are pretty strong. Next, glue the pipe to the union and hold together for about a minute and wipe the excess. Union ends like to push out so hold the two tightly with the union end facing up so any excess glue in the pipe doesn't true to run out, until the glue's grab overcomes the fitting's desire to push out. Unions are made of a slightly different plastic.
If you bought a coupling:
Prime and glue the coupling to the other end of the pipe and wipe away the excess. Reprime the inside of the coupling to remove any drips of glue inside the unglued surface.
Go outside and prime the other end of the pipe that goes to the filter. Cover the pump first! Primer will stain the pump. Close the can tightly and bring it in the house for storage.
If you used the union, attach the other half hand tight
Wrap teflon tape so there are about 4 thicknesses covering the threads of the male adapter. Wrap in a counter clockwise direction so the end of the tape doesn't unravel when you are threading it into the pump. A large set of channel lock pliers or a big monkey wrench will give you the leverage to need to thread it in like the old one was.
Make your final glue joint. Remember to hold the pipe down so it doesn't push out. Let it dry for 24 hours before testing. It's cold out and the glue will take some time to dry thoroughly because of this. If it's 50 degrees or more for 12 hours, you can test for leaks.
HTH,
Scott
PoolGuyNJ