In general, dip coating do not produce a uniform coating, as the lower parts are always coated with thicker layer than the upper part, due to gravity. However, if your coating evaporates rapidly, and you can use a thin coating, you can pool the sample very slow, it helps. 

Good luck. 

So, any other method for me to coat the Foley catheter uniformly in lab? 

Spray coating? 

Painting with a brush? 

thank you!