I used a 12mm polycarbonate base, with a hole cut in for my eheim1250's inlet. Although I had to file the hole a tad bigger, I put epoxy resin on the outide of the pump inlet, and then pushed the pump inlet through the hole. This has worked really well, and no leaks at all. If you put a nice sized ring of epoxy resin all round the outside of the inlet, and then let the pump sit on top of the reservoir (upside down in my case) then you get a nice fillt, and any fluid action will just let the epoxy run down into the cracks anyway.
I then used clear acryllic tube, 76mm ID, 4mm wall thickness, about 300mm length and used a product called plastic weld - not JB weld - this stuff is higly volatile, and works into the join by capilliary action. I used a makeshift pipette to apply the plastic weld to both sides of the tube (inside and out, not back and front, lol) on the polycarbonate base, and it's welded up a nice watertight seam that's been working for months now. The epoxy resin has discoloured where it's visible, but only to a translucent yellow / brown, and only because my water is dyed with flourescein/flourescene however you spell it. anyway, with the res inlet pipe put off center, it makes a nice spirally vortex, and filters out bubbles really well.
