If you on the job, then have a tub to soak them in water then wring out by hand.
Then another tub with fusion clean in for them to soak in, wring out.
You dont want them sopping wet, it will spray everywhere when you get the machine working.
Spray the carpet as well with Fusion Clean.
Get the tubs cheap from Wickes, B&Q etc £5-£7, the very flexi coloured ones. Get different colour, one for dirty water, one for Clean Fusion mix.
If you mean when you get back home - stick them in the washing machine. Dont bother with softner.