You might want to put a little diesel in a glass jar and pour in a little of the car wash and see what happens. My guess is it will go right to the bottom (most likely is water based). If that's the case, it may stay in the bottom of your tank forever, unless of course the intake is low enough to drain it out. If it has collected in the bottom, and does not mix with diesel, the strategy you have laid out above won't work.

Good luck.

__________________
1976 240D
1987 560SL
2007 E320 Bluetec
1998 C280 (now son’s car)
1982 240D Manual - Sold