I'm installing a clothes washer in a basement. There's a 2" drain line running in the wall at about 43" above the basement floor. What is the minimum distance needed between the top of the standpipe and the top of the 2" drain line? I'm planning on using an 18" (x 2") standpipe. I figure the machine should be able to pump up to the top of the standpipe, but want to make it as low as possible. Thanks.