I cant see what you have on the end of the pipe?
I cant recall what its called (and now cant find a photo) but on mine, ive got this little bsp 'cage' thing (mesh filter) but the trouble is the surface area of it is too low, and the holes too small, so it gets blocked way too easily.
I want something on the end of the suction pipe, so as to avoid sucking up snails etc (i never used to have a problem with snails until we moved, and now... they dont half block pipes well!) but have not been able to find something suitable.
Ive considered a washable cartridge filter, but id most like something 'snail proof' on the end of the pipe.