Done a simular job before (commercial kids store), loads of soap residue resulting from bubble machine. Mixed up some defomer as a prespray and sprayed it down on worst areas, aggitated and extracted. Repeated if neccesary and then put down usual pre spray.
Also make a good mix of defomer in a jug 1st and suck it up with the hose to line the pipes, keep checking the machine recovery tank every so often for foaming.
Cheers
J