Cleaning models with water and soap before painting

Cleaning it after you build it will remove all the greasy fingerprints from handling it.  That's what I do.

Ok so it's not useful to put the sprues in the water before modeling?

No, I do not think that is necessary.

I wash everything in detergent and water while it's still on the sprue, using a toothbrush to scrub the pieces.  As you say, it's easier when everything is still attached.  This way, I can make sure I reach all the nooks and crannies.

Before painting, I wipe things down with either rubbing alcohol or even a commercial window cleaner like Windex.  

Maybe it's overkill, but I don't usually have a problem with paint lifting.  I use enamels.

Ditto on what checkmateking02 said. I wash them in a large plastic bowl so that if any parts come loose they don't go down the drain. That's not a sight you want to see, watching a grown man cry. 

Jim 

I wouldn't risk doing it after assembly for fear of washing off loosely glued parts. I've always done it on the sprues..

I am one of the group that washes the parts before I build, using a fish tank net to dip parts into a bowl of water-soap mixture, then to rinse

I only wipe off the finished model with swabs and Q-tips dipped in rubbing alcohol after assembly

even if you do choose to wash in water after assembly,,,,,,don't immerse the model in water,,,,,,,,water gets trapped inside sometimes,,,,,,,,you either end up waiting forever for the model to dry before you paint,,,,,,or you get seepage during the masking or painting stages

wash the model with a brush, or one of those sponges on a stick,,,,,near running water, but not under the stream or in a bowl (I am sure your LHS buds didn't mean dip it in the water)

Rex

I don't think it's necessary to wash them at all,never did,never had any kind of painting problems.

Ok thank you guys for your tips.  I will try to wash my sprues right at the beginning.