I need to cut my main drain line between the valve and the pool to relocate my equipment inside the poolhouse I'm building. The point where I need to cut it is about 18" below the winter water level.

I'm sure I could cut the line and cram a rubber plug in there before the hole filled up, but how can I make a good solvent joint at the cut? Maybe I should have done it when the water was warm and I could have put a bucket over the drain and held it down with the pole.

I've heard that plumbers have a method of freezing the water in a line to allow repairs where the water can't be shut off. Will this work on an inch-and-a-half line?