You're actually better off using a lubricant made for detailing clay as some car wash shampoos will degrade the clay rendering it useless. Having logged the disclaimer, you can try mixing a tbls. of high quility car wash shampoo with about 20 oz. of (distilled) water and test. If it seems the clay is not holding up - stop and go get some QD.
Using detail clay is the best way to reveal a clean, contaminant free surface, HOWEVER, claying is (or can be) an abrasive process that must be done with moderate care to prevent marring.
Detail clay procedure:
1) Wash vehicle well using a good quality car shampoo.
2) Use a bug/tar remover as necessary to get the surface as clean as posible (clay will remove these contaminants, but I prefer to save the clay for those things conventional wash methods don't remove).
3) Remove any rings, watches, etc.
4) Work small sections at a time. Spray clay lubricant liberally and holding the clay bar FIRMLY, gently move clay bar back and forth over the area, floating the clay bar over the lube. Only apply enough pressure to make good contact to make good contact.
5) Use your other hand to feel the surface, moving on if it feels smooth.
6) Follow the detail clay by wiping with a good MF towel (may skip this if you will wash again after claying).
7) As the surface of the clay becomes dirty, fold, kneed and remold the clay bar to reveal a clean surface.
8) You may wish to test the surface by inserting your hand in a regular plastic sandwitch bag and lightly rubbing across the surface. If you feel any bumps, more claying may be needed (Unless close examination reveals some surface defect).
9) Be sure to follow-up the claying process with polishing and or a last step product (LSP) wax or polymer as clay may remove surface ptotection.
Note: If you drop the clay bar it may not be suitable for further use!
