A permutation of the computational geometry drainplug it references, this suits 57mm diameter drainholes. The purpose of the strainer is to efficiently strain fluff and hair from large volumes of water - without the possibility of clogging.

This variant solves the problem of the strainer floating off the drainhole with large water influxes. It does so by including an enclosed volume for a 30mm diameter lead sinker... The additional weight ensures the strainer stays firmly in place in all circumstances.

Video showing structure http://www.youtube.com/watch?v=K16VUzcdnqY

The shell is created with the Grasshopper code from http://www.thingiverse.com/thing:205483. An updated version of the file is included which is slightly more robust than the original code.

The inner core is a simple bit of modelling. Creating "hollow" objects requires a very tiny hole linking the inner and outer portions of the object, otherwise surface based solid modellers like Rhino3D just ignore the interior surfaces. The hole is too small to be modelled in the STL and the inner part is essentially hermetic. The Weaverbird mesh tool has been used to do some laplacian smoothing on the interior model to make it more "organic"; just cosmetic as the improvement on flow characteristics while real will be inconsequential... But why not create nice models if you can eh?

This can be printed without supports. The STL includes a "tear off" warp prevention ring. (a 0.2mm layer about 5mm wide that in my experience completely eliminates the warping caused by laminar convection flows across the HBP)

Just drop in the lead sinker after pausing the print at the appropriate height (i.e. once the walls are high enough to ensure the print nozzle cannot contact the sinker). Voila a robust and high performance drain strainer that will not float off with large water flows...