electric bottle sterilizer...

i just realized that im supposedt to clean my avent electric bottle sterilizer every 4 weeks with citric acid.....ooooops!

my question is where can i find the citric acid? im gonna go to walmart (not super walmart) in a little while....has anyone found it in a regular walmar? is it a liquid or powder or pill?

how the heck and i suppose to clean the sterilizer with this? i bought it off ebay so it didnt come with the box or instructions.

Get from a fruit but i had one of those but it was a micorwave sterilzer. You should have never bought one. Use a dishwisher way better.