What does it do? Prewash what?

This is a prewash for cepap accesories. It cleans off any oils or manufacturing residue. By using the prewash the ionic smell is not so strong.

Can i use a more cost effective pre-wash, such as baby shampoo, for my pap equipment's initial setup as i have several items to clean?

Hello, you can use a dye free, scent free, lotion free detergent in place of the Pre-Wash if needed.

Do you use this solution with the soclean machine , or prewash it without using the soclean machine.

Only use the solution to pre-wash and then rinse and let dry.Never put any cleaning solution in the machine. Just keep the filters changed every six months as needed.

How often you need to use this? Only before forst use with the so clean or more?

Only when you get new mask and hose your supposed to wash it before you start using it. Initialy I washed the mask, hose, and water storage. I only put it in the So Clean every 3 nights after I fill the reservoir with water so it cleans the water also. You can put it in and clean it every day if you want. I just did not always remember. I will put it in the machine after I just get up and it is set to start @10:00 am it takes about 2hrs to complete. The machine makes a humming noise for the short time in my case 7 mins and then no noise for the rest of the 2 hrs. It is factory set to 7 mins. but you can change it. The mask smells clean and fresh like fresh air after a rain storm. This machine is great it was a pain in the ---- when you had to wash it every day or every night. I would probably clean once every 2 weeks. Now it is every 3 days and it is clean and I fell great. Let me know if you have any other questions. This is second best purchase after only the CPAP machine. Order from Amazon as you get the water tank lid that the SoClean 2 web site charges you, save money and it makes you feel even better.