How do I Keep taped lines while wet sanding?

You don't wet sand with the tape applied. At least I never have. Let the paint dry completely. I use a polishing stick with water and a drop of dish soap to suspend the paint particles.

 

If you're wet sanding between coats like many top painters do, you have to sand with the masking tape on unless you're going to re-mask after every coat; which would be a pain.

Popcop45 wrote:

If you're wet sanding between coats like many top painters do, you have to sand with the masking tape on unless you're going to re-mask after every coat; which would be a pain.

I don't see any other alternative as the sand paper is going to remove the tape regardless of what precautions you use. I would just give it several coats then use a product like the Micro Mesh polishing set that has sandpaper up to 12,000 grit and dry sand it. 

Yeah I agree with Mike, put your color coats down then remove the tape and polish.

MikeV wrote:

Popcop45 wrote: If you're wet sanding between coats like many top painters do, you have to sand with the masking tape on unless you're going to re-mask after every coat; which would be a pain. I don't see any other alternative as the sand paper is going to remove the tape regardless of what precautions you use. I would just give it several coats then use a product like the Micro Mesh polishing set that has sandpaper up to 12,000 grit and dry sand it.

Fingernail polishing sticks offer similar grits for far less money...modelers are a frugal bunch. In fact the polishing sticks that I use and at one time sold, were from Micro Mesh. 

Another alternative, and I am assuming this person wants glossy automotive paint jobs, is to use urethanes like some modelers do. These are the paints you see used on custom cars and choppers and they are gorgeous once clear coated. The problem is that the paints are expensive although Coast Airbrush sells them in small quantities. You need very good ventilation for the clears though as they are isocyanates and you do not want them entering your eyes, nose, ears or any other opening.