How to remove a huge Plecostomus from a 29gallon fish tank?

I have 2 huge 6-8 inch Plecostomuses. I'm planing to either sell them or retank them when I buy a better sized tank. The problem is, how the heck do I take them out. I have two small fish nets (the little tiny net to get small fish). But they're no match for the Plecostomuses, 1x1" square net. Do I use a small plastic shoebox and catch them? Or do I grab them out by hand? I have no idea. These are my second/third Plecostomuses (the first one died VERY young). Please tell me before I sell/retank them! 10 points for best answer.