Need specific help with a TFK Twinner Twist!

[firsttimetwins]

We have just bought a second-hand TFK Twinner Twist. It's in good condition but needs a wash. According to the label, the removable buggy bit is machine washable. However, it is kept in shape at the back and the seats with plastic inserts. The back inserts remove easily via a velcro opening, but we just can't find an opening to get the seat inserts out. Any ideas? These inserts might wash ok, but the whole thing won't fit in the washing machine with the inserts in! Thanks!