I just got the same washer about a week ago (Kenmore HE3t). I got the neptune dryer instead of the matching dryer. Someday you're going to read about me in the paper - I love sitting in front of the washer and watching it run - it is so cool!
Anyhow - I do a prewash separate from the wash cycle (the 21 minute cycle), because I remember reading if you do a prewash integrated into the wash cycle (I use sanitize with my dipes), the prewash will be the same temp as the wash cycle (160 for the sanitize cycle). If you do the prewash separate, it will be cold water. The only reason I like to do a cold prewash is because a lot of women here seem to like doing a cold prewash (I should note, I'm at day 12 of CDing my 15mo).
I'm going to try to add the liquid calgon in my next wash load - I'll put it in with the powdered tide and see what happens. The question for me is how much to use. We have moderately soft water - so I guess I'll just use a bit and work my way up.
I use 4T of tide he on a huge load (like a double comforter) and usually use 1T - 2T on dipes (in part because I don't fill up the machine - don't have that many yet!).
The crazy thing I noticed today - when I washed some hemp terry I just got to make liners - was that despite not using any soap, the fabric came out smelling like the tide he I've been using! I'm wondering if this means that there's build up in my machine.
[For you more experienced mammas: Does powdered calgon exist? If so, where can I get it in northern Virginia? (The liquid stuff was practically hidden at walmart) Any place to order it on line?]